A full 15 L scuba tank at 295 K contains 144 moles of air and has a pressure of 234 atm. At the end of the dive, the tank has a pressure of 68 atm and a temperature of 280 K. How many moles of air are left in the tank?

a. 56 moles

b. 48 moles

c. 72 moles

d. 64 moles