the complete question is
Two storage sheds are to have the same area. One is square and one is rectangular. The rectangular shed is 3 meters wide and 12 meters long. How large is one side of the square shed in meters?
we know that
area of the rectangular shed =L*W-------> 12*3=36 m²
area of the square shed=b²
area of the square shed=36 m²
so
b²=36
b=√36
b=6 m
the answer is
the large of the square shed is 6 meters