fill the blank with the preterite tense of the verb in parentheses.
usted a la tienda por teléfono. (llamar) (1 point)
2.
fill the blank with the preterite tense of the verb in parentheses.
los alumnos no anoche. (estudiar) (1 point)
3.
fill the blank with the preterite tense of the verb in parentheses.
ella la guitarra anoche. (tocar) (1 point)
4.
fill the blank with the preterite tense of the verb in parentheses.
los señores a la banda ayer. (escuchar) (1 point)
5.
fill the blank with the preterite tense of the verb in parentheses.
nosotros español. (estudiar) (1 point)
6.
fill the blank with the preterite tense of the verb in parentheses.
yo a colombia . (viajar) (1 point)
7.
fill the blank with the preterite tense of the verb in parentheses.
tú con susana en la fiesta anoche. (cantar) (1 point)
8.
fill the blank with the preterite tense of the verb in parentheses.
yo a las cinco y media. (empezar) (1 point)
9.
change this verb from the present tense to the preterite tense.
yo empiezo (1 point)
10.
change this verb from the present tense to the preterite tense.
ella empieza (1 point)
11.
fill the blank with the preterite tense of the verb in parentheses.
yo una buena nota. (sacar) (1 point)
12.
fill the blank with the preterite tense of the verb in parentheses.
8. tú una buena nota. (sacar) (1 point)
13.
change this verb from the present tense to the preterite tense.
yo pago (1 point)
14.
change this verb from the present tense to the preterite tense.
ellos lavan (1 point)
15.
change this verb from the present tense to the preterite tense.
tú lavas (1 point)
16.
change this verb from the present tense to the preterite tense.
usted manda (1 point)
17.
change this verb from the present tense to the preterite tense.
ustedes lavan (1 point)
18.
change this verb from the present tense to the preterite tense.
yo mando (1 point)
19.
change this verb from the present tense to the preterite tense.
raúl estudia (1 point)
20.
change this verb from the present tense to the preterite tense.
yo hablo (1 point)
 description

1) Usted llamó a la tienda por teléfono. This task requires you to use your knowledge of the tense called preterite that is needed to describe an action that was completed at some moment in the past. It has its own structure of how to make up a preterite verb out of an infinitive. All the infinitives that stand with the subjects él, ella, usted end with -ar will change the ending to -o. 

2) Los alumnos no estudiaron anoche. The most important thing when changing tenses into preterite one is to pay attention to the subject because the ending of the verb strictly depend on it. As you can see, the subject is 'students' which is a pronoun 'they'. In such cases you have to add ending -aron to the infinitive. 

3) Ella tocó la guitarra anoche. In this sentence the subject is 'she'. According to the grammar table of preterite tense, the verb that belong to the subjects (pronouns) like he/she/ change its ending into -ó.  Keep in mind that you use ending -o only with the infinitives that have ending ar.

4) Los señores escucharon la banda ayer. The subject of this sentence is 'señores' (gentlemen) that is a third person plural pronoun. When you have such pronouns serving as the subject, the infinitive's ending must be changed into -aron (when the ending of infinitive is -ar).

5) Nosotros  estudiamos español. This sentence contains the first person pronoun, or subjective pronoun because it serves as the subject of the sentence - 'We'/'Nosotros'. If the infinitive that belongs to subject 'nosotros' has ending -ar its ending must be changed into -amos in order to make preterite verb out of it.
6) Yo viajé a Colombia. The subject of this sentence is a first person pronoun 'I'/'Yo'. In preterite tense, when a verb stands near this subject in the sentence it changes its ending into -é or -í. Since the infinitive form of the verb ends with 'ar' its preterite ending must be -é.

7)  Tú cantaste con Susana en la fiesta anoche. Be careful and don't confuse the subject of the sentence with its object. The subject of this one is 'You'/'Tú'/ and the object is 'Susana'. The infinitives that stand near second person pronoun 'tu' and end with -ar change their endings into -aste to form preterite tense.

8)  Yo emprezé a las cinco y media. As you can see, the first person pronoun 'Yo'/'I' plays the role of the subject of this sentence. The infinitive form of the given verb ends with -ar, therefore in order to form the preterite tense you have to change this ending into -é.

9)  Yo empecé. The verb 'empezar' means 'to begin'. In Spanish it has some peculiarities that you have to learn by heart. It is a stable grammar point as it is orthographically changinf verb : when forming a preterite tense and the subject is first person pronoun 'I' this verb will be 'empecé'. 

10) Ella empieza=EMPEZÓ. (The infinitive of this sentence is empezar.)As you can see, the subject of this sentence is Ella, which is second person pronoun, and when the subject is /él/ella/ usted the infinitive of the verb that belongs to it always changes its ending (-ar) to (-ó).

11) Yo saqué una buena nota. The verb 'sacar' is orthographic changing verb, and when it stands near the subject that is a first person pronoun "I\To'' it does not just changes its infinitive ending into -é, it completely changes into 'saqué'.

12) Tú sacaste buena nota. In this case you have to follow standard grammatical rules of forming preterite tense because this sentence starts from 'You'/'Tú/. The subject of this sentence is second person pronoun, so the preterite form of the verb must be sacaste (with added ending 'aste').

13) Remember that when the Spanish verb 'pago'  is used with the first person pronoun in singular 'I' it changes into pagué when forming preterite tense. It happens because this verb belongs to the list of orthographic changing verbs.

14) Ellos lavaron. The subject of this sentence is third person in plural 'they,ellos/. Since the infinitive form of the verb 'wash' is 'lavar', its ending (-ar) changes into -aron that is always added to the verbs that belong to subjects ellos, ellas and ustedes.

15) The preterite form of this sentence is: Tú lavaste. The infinitive form of the verb is lavar, as was mentioned in the previous answer. In this case we have another subject which second person pronoun 'you/tú'. The ending of the infinitive (-ar)  changes to -aste when it belongs to second person pronoun.

16) The preterite form of this sentence is: Usted mandaró. With the pronoun 'usted' you can't use the same ending of infinitive as you used with the pronoun 'tú'. Both these words mean 'you', but 'usted' is more respectful and polite. When it stands as a subject of the sentence, the verb 'mandar' changes its ending into -ó.

Right your are correct