12.21 Air at a pressure and temperature of 100 in. of mercury absolute and 100 F, respectively, discharges at a rate of 5 lbm/s from a tank through a convergent-divergent nozzle into another tank maintained at a pressure of 20 in. of mercury. Determine the nozzle throat and exit diameters for full expansion. Determine the pressure, temperature, velocity in the throat, and the Mach number at the nozzle exit.