Answer:
72 sq cm
Explanation:
For any rectangle, the diagonal is the hypotenuse of the right triangle formed by the base of the rectangle(b) and the height (h) of the rectangle
By the Pythogorean formula

where d is the diagonal
For a square, all sides are equal so b = h = a and we get the formula


In this case we have d =12 so

But for a square of side a, the area is
so 72 is the area