For path iaf, Q = 50 cal W = 20 cal By first law of thermodynamics, ΔU = Q - W = 50 - 20 = 30 cal. For path ibf
Q' = 36cal W = ? or, W' = Q' - ΔU Since, the change in internal energy does not depend on the path, therefore ΔU ’ = 30 cal ∴ W' = Q’- ΔU '= 36 - 30 = 6 cal.