Answer
$11.3ft$
Work Step by Step
The volume of the cylinder is $v1=\pi r^2 h=30\pi r^2$ where r is the radius,
the volume of the hemisphere is $v2=\frac{1}{2}\times\frac{4}{3}\pi r^3$.
The total volume v1+v2 is known and lead to the equation
$\frac{2}{3}\pi r^3+30\pi r^2=15000$
Solve the equation numerically gives the positive radius as $r=11.3ft$
