Calculate $5$ to the power of $7$ and get $78125$.
$$y=\frac{3}{2}\sqrt{78125}$$
Factor $78125=125^{2}\times 5$. Rewrite the square root of the product $\sqrt{125^{2}\times 5}$ as the product of square roots $\sqrt{125^{2}}\sqrt{5}$. Take the square root of $125^{2}$.
$$y=\frac{3}{2}\times 125\sqrt{5}$$
Multiply $\frac{3}{2}$ and $125$ to get $\frac{375}{2}$.
