The central angle of a regular pentagon measures 360/5=72°.
Two 3' radii and a side of the pentagon form an isosceles triangle, the base of which is 2×3sin36=6sin36=3.5267' approx. So the perimeter measures 5×6sin36=30sin36=17.6336' approx.
The area of the isosceles triangle=32sin72°/2=4.2798ft2 approx, making the area of the pentagon 5 times this: 21.3988ft2.