a
for cyclic process
$\mathrm{dQ}=\mathrm{d} \mathrm{W}$
$\Rightarrow \mathrm{d} \mathrm{Q}=\frac{1}{2} \times 200 \times 100 \times 10^{-6} \times 10^{3} \mathrm{J}=10 \mathrm{Joule}$
also $dQ$ $=2.4 \mathrm{cal}$
$\Rightarrow \mathrm{J}=\frac{10}{2.4}=4.17 \mathrm{J} / \mathrm{cal}$