b
(b)
Initial volume $V=(\text { side })^3=\left(10 \times 10^{-2}\right)^3$
$P=7 \times 10^6 \,Pa$
$B=140 \times 10^9 \,Pa$
We know
$\frac{-\Delta V}{V}=\frac{P}{B} \quad\{-\Delta V=\text { Contraction in volume }\}$
$\frac{-\Delta V}{10^{-3}}=\frac{7 \times 10^6}{140 \times 10^9}$
$-\Delta V=5 \times 10^{-8} \,m ^3$