Consider 5.5 L of a gas at a pressure of 3.0 atm in a cylinder with a movable piston. The external pressure is changed so that the volume changes to 10.5 L.
a) Calculate the work done, and indicate the correct sign.
b) Use the preceding data but consider the process to occur in two steps. At the end of the first step, the volume is 7.0 L. The second step results in a final volume of 10.5 L. Calculate the work done, and indicate the correct sign
c) Calculate the work done if after the first step the volume is 8.0 L and the second step leads to a volume of 10.5 L. Why work not state function

Question

Consider 5.5 L of a gas at a pressure of 3.0 atm in a cylinder with a movable piston. The external pressure is changed so that the volume changes to 10.5 L. 
a) Calculate the work done, and indicate the correct sign.
b) Use the preceding data but consider the process to occur in two steps. At the end of the first step, the volume is 7.0 L. The second step results in a final volume of 10.5 L. Calculate the work done, and indicate the correct sign
c) Calculate the work done if after the first step the volume is 8.0 L and the second step leads to a volume of 10.5 L. Why work not state function

aaronq · Answer

you can find the pressure after volume change with $P_1V_1=P_2V_2$ 
but i don't know how you can find the external pressure to use  $W=-P\Delta V $