Air is heated as it flows through a 6 in 6 in square duct with negligible

Question:

Air is heated as it flows through a 6 in × 6 in square duct with negligible friction. At the inlet, air is at
T1 = 700 R, P1 = 80 psia, and V1 = 260 ft/s. Determine the rate at which heat must be transferred to the air to choke the flow at the duct exit, and the entropy change of air during this process.