When a system is taken from state i to a state f along path iaf, Q = 50J and W = 20 J. Along path fbi, Q = 35J. If w = – 13J for the  return path fi, Q for this path is

For the process i - a - f, Q = +50 J, W = +20 J.Now by 1st law of thermodynamics, Q = ΔU + W.⇒(Uf - Ui) = +30 JFor the return path fi,W = -13 J, Ui - Uf = -30JBy 1st law of thermodynamics.Q = (Ui - Uf) + W = -30 + (-13)⇒Q = -43 J.