Given, heat, Q=−30J Work done on the gas, W=−10J Initial internal energy, Ui=−10J Final internal energy, Uf= ? According to first law of thermodynamics, Q=W+∆U ⇒−30=−10+Ui−Uf ⇒−30=−10−10−Uf ⇒30=10+10+Uf ⇒30−20=Uf ⇒Uf=10J