A fan operates at a temperature of 70°F and a pressure of 1 atm. The fan moves air at 3000 ft/min against a static pressure of 0.02 psig through a 2 ft diameter duct. The fan speed is increased by 30%, whereas the air properties remain the same. The horsepower delivered to the air by the fan is
a. 2.5 hp
b. 3.1 hp
c. 3.6 hp
d. 4.2 hp