We have a trampoline with 21ft of diameter so we can calculate the radius like:
[tex]r=\frac{D}{2}[/tex]so if we solve it will be:
[tex]\begin{gathered} r=\frac{21}{2} \\ r=10.5 \end{gathered}[/tex]Now we can use the formula for the area of a circle that is:
[tex]A=\pi r^2[/tex]so:
[tex]\begin{gathered} A=3.14\cdot(10.5)^2 \\ A=346.185 \end{gathered}[/tex]