Answer
4 in.
Work Step by Step
diameter = 2 r = $\frac{3}{4}$ h
r = $\frac{3}{8}$ h
Volume = $\pi$ $r^{2}$ h
9 $\pi$ $in.^{3}$ = $\pi$ $(\frac{3}{8} h)^{2}$ h
9 $\pi$ $in.^{3}$ = $\frac{9}{64}$ $\pi$ $h^{3}$
$h^{3}$ = 64 $in.^{3}$
h = 4 in.
