Answer
Please see the work below.
Work Step by Step
We know that
$P=\frac{mgh}{t}$
This can be rearranged as:
$\frac{m}{t}=\frac{P}{gh}$
We plug in the known values to obtain:
$\frac{m}{t}=\frac{(0.5hp)}{(60m)(9.8\frac{m}{s^2})}=\frac{(0.5hp)(746\frac{W}{hp})}{(60m)(9.8\frac{m}{s^2})}=0.63\frac{Kg}{s} = 10.1 \frac{gal}{min}$
