If (2a) (2b)= 128, what is a + b equal to?
a. 1
b. 6
c. 7
d. 12

First we try to simplify it as much as we can:
2*2*a*b = 128
4ab = 128
then divide both sides by 4
ab = 32

now, we want to think - "What two numbers multiply to 32?"
that would be the pairs of factors of 32
this is:
1, 32
2, 16
and
4, 8

now, which of those pairs adds up to one of your options?
1 + 32 = 33
2 + 16 = 18
4 + 8 = 12

12 is one of your options, therefore that is your answer!