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!