The air supply to an engine on a test bed passes down a 180 mm diameter pipe fitted with an orifice plate 90 mm diameter. The pressure drop across the orifice is 80 mm of paraffin. The coefficient of discharge of the orifice is 0.62 and the densities of air and paraffin are 1.2 kg/m³ and 830 kg/m³ respectively. Calculate the mass flow rate of air to the engine.