The formula to find the area of a circle is
[tex]\begin{gathered} A=\pi r^2 \\ \text{ Where A is the area and} \\ r\text{ is the radius of the circle} \end{gathered}[/tex]So, in this case, you have
[tex]\begin{gathered} r=21ft \\ \text{ Because} \\ \text{radius =}\frac{\text{ diameter}}{2} \\ \text{radius =}\frac{42ft}{2} \\ \text{radius =}21ft \end{gathered}[/tex][tex]\begin{gathered} A=\pi(21ft)^2 \\ A=\pi\cdot441ft^2 \\ A=1385.44ft^2 \end{gathered}[/tex]Therefore, the area of this circle is 1385.44 square feet.
