Answer
$57KJ$
Work Step by Step
We know that the change of internal energy is given as:
$\Delta U=nC_v\Delta T$
We plug in the known values to obtain:
$\Delta U=(21)(\frac{3}{2})(8.314)(160)$
$\Delta U=42KJ$
Now we can find the required work done as
$W=Q-\Delta U$
We plug in the known values to obtain:
$W=-15-42=-57KJ$
