Answer
$27$ square miles.
Work Step by Step
The given function is
$\Rightarrow f(x)=29x^{\frac{1}{3}}$
$f(x)=87$.
Substitute the value of $f(x)$ into the given function.
$\Rightarrow 87=29x^{\frac{1}{3}}$
Divide both sides by $29$.
$\Rightarrow \frac{87}{29}=\frac{29x^{\frac{1}{3}}}{29}$
Simplify.
$\Rightarrow 3=x^{\frac{1}{3}}$
Cube both sides.
$\Rightarrow (3)^3=(x^{\frac{1}{3}})^3$
Simplify.
$\Rightarrow 27=x$
Hence, the area is $27$ square miles.
