Given that, heat released, ΔQ=−30J Work done on the gas, ΔW=−18J Change in internal energy =ΔU Initial internal cnergy, Ui=60J Let final internal energy, Uf=U By using first law of thermodynamics, ΔQ=ΔW+ΔU Substituting the values, we get −30=−18+(Uf−Ui) −30+18=U−60 ⇒U=48J Hence, the final internal energy of gas is 48J.