Aword or a phrase that is informal and particular to certain time periods or social situations is called

Colloquialism

Explanation:

Colloquialism is a variation of popular language used in more informal everyday situations, ie colloquialism is the use of informal language in certain time periods or social situations. Colloquiality finds fluency in orality (speaking) and thus does not require adaptation to the norms of traditional grammar (cultured norm / standard of the Portuguese language). It is in the colloquial language that we find the slang words, foreign words, neologisms, abbreviations, that is, words and expressions that are not related to the educated norm of the Portuguese language.

8 - (2a + 7) = a + 40     distribute/multiply - into (2a + 7)

8 - 2a - 7 = a + 40

1 - 2a = a + 40       add 2a on both sides

1 = 3a + 40         subtract 40 on both sides

-39 = 3a       divide 3 on both sides

-13 = a

[proof]

8 - (2a + 7) = a + 40

8 - (2(-13) + 7) = -13 + 40

8 - (-26 + 7) = 27

8 - (-19) = 27

8 + 19 = 27

27 = 27