The pressure drop in a venturi meter (Fig. P3.128) varies only with the fl uid density, pipe approach velocity, and diameter ratio of the meter. A model venturi meter tested in water at 20 8 C shows a 5-kPa drop when the approach velocity is 4 m/s. A geometrically similar prototype meter is used to measure gasoline at 20 8 C and a fl ow rate of 9 m 3 /min. If the prototype pressure gage is most accurate at 15 kPa, what should the upstream pipe diameter be