In order to find the radius of the circle use the following formula for the area of a piece of circle with a given central angle:

in this case you have:
A = 20 ft²
θ = 40°
r = ?
first, solve for r in the given formula and then replace the value of A:
![\begin{gathered} r=\sqrt[]{(360)/(\theta\pi)A} \\ r=\sqrt[]{(360)/(40\pi)(20)}ft\approx7.6ft \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/72up8fxljpcazg0i842bwrgrnu25uygbmo.png)
Hence, the radius of th cricle is r = 7.6 ft