1. The problem statement, all variables and given/known data Given: A scuba diver has a tank with an internal volume of 2500 cm^3 air tank which is pressurized to 22 MPa at 27 deg C. After diving for 20 minutes, she notices that the air pressure has reduced to 6 MPa while the temperature of the tank has dropped to 18 deg C. Find: What is the mass of air that the diver has breathed through her lungs during the dive? 2. Relevant equations P2*V2/T2 = P1*V1/T1 or Pv=nRT ? 3. The attempt at a solution I'm confused which equation we use to find the solution and from there on how to punch in all the numbers to get to the solution. I know the volume of air is 0.0883 m^3/Kmol, Rair = 0.2870 KJ/Kg*K, and mass = 28.97 kg/kmol Also R = 8.314 KJ/Kg*K I'm just really confused on where everything goes into play and why?