the answer:
12 inch
the explanation:
the formula for an area is:
area=height ×width
138=?×?
it's a square so both unknown values have to be the same.
to find out that value you have to square root it
√(138)=11.7473401245
11.7473401245×11.7473401245=138in
round the number off and you have 12 inches