A popular size of scuba-diving tank holds the amount of compressed air that would occupy 71.2 ft3 at a normal surface pressure of 1 atm. The air in the tank is at a pressure of about 2250 lb/in.2, so the tank itself can have a volume much less than 71.2 ft3. How large does the tank need to be to hold 71.2 ft3? (Hint: Use Boyle’s Law: PV 5 k. Remember that 1 atm 5 14.7 lb/in.2.)
I dont understand this, help please!

Question

A popular size of scuba-diving tank holds the amount of compressed air that would occupy 71.2 ft3 at a normal surface pressure of 1 atm. The air in the tank is at a pressure of about 2250 lb/in.2, so the tank itself can have a volume much less than 71.2 ft3. How large does the tank need to be to hold 71.2 ft3? (Hint: Use Boyle’s Law: PV 5 k. Remember that 1 atm 5 14.7 lb/in.2.) 
I dont understand this, help please!