\(P _{1}- P _{2}=4500\,Pa\)
\(P _{1}+\frac{1}{2} \rho V _{1}^{2}+\rho gh = P _{2}+\frac{1}{2} \rho V _{2}^{2}+\rho gh\)
\(P _{1}- P _{2}=\frac{1}{2} \rho\left( V _{2}^{2}- V _{1}^{2}\right)\)
And \(A _{1} V _{1}= A _{2} V _{2}\)
\(\Rightarrow \quad V _{2}=2 V _{1}\)
\(4500=\frac{1}{2} \times 750 \times 3 V _{1}^{2}\)
\(V _{1}=2\,m / s\)
Volume flow rate \(= A _{1} V _{1}=24 \times 10^{-3}\,m ^{3} s ^{-1}\)