$(1)$
\[
\begin{align}
W&=p\Delta V\\
&=0.6\times10^6 \times(4.3-1.5)\\
&=1.68\times10^6\,\rm{J}=1.68\,\rm{MJ}
\end{align}
\]
$(2)$
\[
\begin{align}
\Delta U&=Q-W\\
&=350\times10^3-1.68\times10^6\\
&=-1.33\times10^6\,\rm{J}=-1.33\,\rm{MJ}
\end{align}
\]
