The change in internal energy of the system is that there is an increase of 306kj in internal energy. By using the first law and sign convention; ΔE₍int₎ = Q - W But Q₍int₎ greater than 0 W₍int₎ less than 0 in convention So, ΔE₍int₎ = Q - W = 186 - (-120) = 186 + 120 =306 kj