When you learn a new noun, learn the verb(s) that is usually used with it. A good dictionary will give an example of the correct verb to use. Tick the correct verb, make or do, for each noun.

1 ) a + b = 12

Периметр можно найти по формуле P=2(a+b) = 2 * 12 = 24

2 ) P = 16

По обратной формуле найдём a+b :

16 = 2(a+b)

a+b = 8