An orifice meter is to be installed in a 12-in ductile iron pipe carrying water at 60°F. A mercury manomoter is to be used to measure the pressure difference across the orifice when the expected range of the flow rate is from 1500 gal/min to 4000 gal/min. The manometer scale ranges from 0 to 12.0 in of mercury. Determine the appropriate diameter of the orifice.