Problem # $9$

Two large water reservoirs are going to be connected by $786ft$ of pipe. The pressure in one reservoir is $28\mathrm{.}5$ psig and its level is $325ft$ above the level of the other one which operates at $17\mathrm{.}5g.$ Water will flow steadily through the pipe.

What size pipe should we choose if we wish to have $325gpm$ flowing through the pipe?