Answer
-67200 J
Work Step by Step
Internal energy $\Delta U=q+w$ where $q$ the heat transferred and $w$ is the work done.
Work received by the system is positive and work performed by the system is negative.
Here, work is performed by the system.
Therefore, $w=-720.\,L\cdot atm=-720.\,L\cdot atm\times\frac{101.325\,J}{1\,L\cdot atm}=-72954\,J$
Heat absorbed is positive and heat released is negative.
As heat is absorbed,
Heat transfer $q=+5750.\,J$
So, $\Delta U=(5750\,J)+(-72954\,J)=-67200\,J$
