How Are Questions inside Questions Called?

English as a Second Language English Vocabulary, Grammar and Idioms
#1

Hi Forum,
If there is a math test that looks as follows:

  1. Solve 2x + 3 = 0.
    a. Using the value of x, calculate (x + 9).
    b. Calculate (9x)

(1) Would be called the “question”, how would (a) and (b) be called? Subquestion? Something else?

Thanks!

#2
  1. I reckon you’d call that “an equation”, rather than “a question”
  2. Probably additional tasks