(poder) ir a la excursión con ustedes? aunque (although) tengo que volver a mi casa a las tres. gabriela no, no (2) (poder) venir. nosotros (3) (pensar) salir a las doce. alejandro yo (4) (querer) ir. ¿(5) (poder) ustedes volver a las dos?

The first answer is "Puedo."

"Poder" (an irregular verb) is conjugated in first person present tense to "puedo," so the sentence will read: Can I go on the excursion with you? We can infer from the rest of the sentence that this person is asking for permission to do something with other people, which is why first person make sense.

The second answer is "puede."

This verb conjugation corresponds to Gabriela, who is in the third-person singular box (if you're not sure, change "Gabriela" to "she"). The sentence will read: Gabriela cannot come.

The third answer is "pensamos."

"Nosotros" signifies first-person plural, so we know the ending is going to be -amos. Although "pensar" usually means "to think," in this case it means "to plan," so the sentence will read: We plan to leave at 12.

The fourth answer is "queremos."

Assuming that the sentence says "Alejandro y yo," this signifies another first-person plural conjugation (if you're not sure, change "Alejandro and I" (Alejandro y yo) to "us" (nosotros)). Since "querer" is an -er verb, the conjugation ending will be -emos.

The fifth answer is "pueden."

This verb corresponds to the word "ustedes" (you plural), which is a third-person plural conjugation. The ending is thus -en, and the sentence will read: Can you return at 2?

Procedural is the answer.  hope that ! : )