The internal energy change in a system that has absorbed

The internal energy change in a system that has absorbed 2 kcals of heat and done 500 J of work is :

According to first law of thermodynamics Q = ∆U + W
∆U = Q – W
= 2 × 4.2 × 1000 – 500
= 8400 – 500 = 7900 J