$P v^{\gamma}=$ constant $\Rightarrow v d P+P \gamma d v=0 \Rightarrow \frac{d P}{d v}=-\frac{\gamma P}{v}$
For $P=0.7 \times 10^{5} N m^{-2}, v=0.0049 m^{3}, \gamma=1.4$
required slope $=-\frac{1.4 \times 0.7 \times 10^{5} N m^{-2}}{0.0049 m^{3}}=-2 \times 10^{7} N m^{-5}$

