thermodynamic changes?

Question

Steam expands in a cylinder with a sliding piston in a steam engine. The resisting pressure, Pext, is
78947 Pascals, the volume changes from 187.5 L to 89.2 L, and 3550 J of energy is lost to the surroundings as heat. Calculate the change in energy of the steam in Joules.

Answer 1

Total energy = q+w = -Pext x deltaV
w = -Pext x deltaV - q
w = -78,947 J/m^3 x (89.2-187.5 m^3) - 3550 J
= 7.76 x 10^6 J