A 4 in. sch 80 pipe carries water from a storage tank on top of a hill to a plant at the bottom of the hill. The pipe is inclined at an angle of $20^{\circ}$ to the horizontal. An orifice meter with a diameter of $1 \mathrm{in}$. is inserted in the line, and a mercury manometer across the meter reads $2 \mathrm{in}$. What is the flow rate in gpm?