Calculate frequency of revolution of electron in 4th Bohr orbit of ${\mathrm{Be}}^{+3}$ ion

Given that $\frac{{\pi }^{2}m{e}^4{k}^2}{h^3}=1.62\times {10}^{15}{\sec }^{-1}$; symbols have usual meaning.

Express your answers in terms of ${10}^{15}{\sec }^{-1}$. Write the answer upto one significant figure.