Answer
$+2.8\times10^{4}J$
Work Step by Step
Let's apply the first law of thermodynamics $Q=\Delta U+W$ to find the change in the internal energy of the system.
$$Q=\Delta U+W=>\Delta U=Q-W$$
Let's plug known values into this equation.
$$\Delta U=+7.6\times10^{4}J-(+4.8\times10^{4}J)=+2.8\times10^{4}J$$
The internal energy of the system increases (+ sign in $\Delta U$)
