A sample of an ideal gas is taken through the cyclic process ABCA as shown in figure. It absorbs, 40 J of heat during the part AB , no heat during BC and rejects 60 J of heat during CA . A work 50 J is done on the gas during the part $B C$. The internal energy of the gas at $A$ is 1560 J . The work done by the gas during the part $C A$ is: