Well, the perimeter of the square is 72/2 = 36 inches = p. The sides of the square are thus p/4 = 36/4 = 9 inches. So what is the area of the square?

Similarly the circumference of the circle is 72/2 = 36 inches. Now recall the perimeter of the square: p = 36 inches. Thus C = 2 (pi) r = p.

Can you finish this?

-Dan