Air flows through a venturi meter with a 3-in.-diameter throat placed in a 6-in.-diameter line. Assume that the upstream pressure is \(60 \mathrm{psi}\) and the temperature is \(68^{\circ} \mathrm{F}\). Determine the maximum possible mass flow rate of air for which the assumption of incompressible flow is a valid engineering approximation. Compute the corresponding differential pressure reading on a mercury manometer.