Figure P$15\mathrm{.}1$

$15\mathrm{.}2$ The diameter of the discharge side of a pump is $6$ in$,$ and that of the intake pipe is $8$ in $($Fig$.$ P$15\mathrm{.}1).$ The pressure gage at discharge reads $30,$ and the vacuum gage at intake reads $10$inHg. If $Q=3\mathrm{.}0cfs$ of water and the brake horsepower is $35\mathrm{.}0,$ find the efficiency of the pump. The intake and discharge are at the same elevation.