Factor $125=5^{2}\times 5$. Rewrite the square root of the product $\sqrt{5^{2}\times 5}$ as the product of square roots $\sqrt{5^{2}}\sqrt{5}$. Take the square root of $5^{2}$.
$$7\sqrt{5}+6\times 5\sqrt{5}$$
Multiply $6$ and $5$ to get $30$.
$$7\sqrt{5}+30\sqrt{5}$$
Combine $7\sqrt{5}$ and $30\sqrt{5}$ to get $37\sqrt{5}$.
