Answer
(600 - 144$\pi$) = 147.61 $ft^{2}$
Work Step by Step
The area of the rhombus whose diagonals have length d1 and d2 is given by A = $\frac{1}{2}$d1*d2
= $\frac{1}{2}$ * 30 * 40
= 600 $ft^{2}$
The area of circle whose radius is A = $\pi r^{2}$
=$\pi (12)^{2}$
=144$\pi$
The area of shaded region = area of rhombus - area of circle
= (600 - 144$\pi$) = 147.61$ft^{2}$
