d
$B=\frac{\Delta P}{\left(-\frac{\Delta V}{V}\right)}$
$\Rightarrow \Delta \mathrm{P}=\mathrm{B}\left(-\frac{\Delta \mathrm{V}}{\mathrm{V}}\right)$
$\Rightarrow \Delta \mathrm{P}=\left(2100 \times 10^{6}\right)\left(\frac{0.004}{100}\right)$
$\left(\text { As }-\frac{\Delta \mathrm{V}}{\mathrm{V}} \times 100=0.004\right)$
$\Rightarrow \Delta \mathrm{P}=84 \times 10^{3} \mathrm{P}_{\mathrm{a}}$