First we try to simplify it as much as we can:
22a*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!
