\(2 P_0=P_0+\rho g h\)

\(\Rightarrow P_0=\rho g h\)

\(\Rightarrow P_0=75 \,cm \text { mercury } \quad \text { [Atmospheric pressure] }\)

\(\Rightarrow \rho_{\text {mercury }} \times g \times \frac{75}{100}=\rho_{\text {water }} \times g \times h\)

\(\Rightarrow \frac{\rho_m}{\rho_w} \times \frac{75}{100}=h\)

\(\Rightarrow \frac{40}{3} \times \frac{75}{100}=h \quad\left[\because \frac{\rho_m}{\rho_w}=\frac{40}{3} \text { (given) }\right]\)

\(\Rightarrow h=10 \,m\)