Factor $12=2^{2}\times 3$. Rewrite the square root of the product $\sqrt{2^{2}\times 3}$ as the product of square roots $\sqrt{2^{2}}\sqrt{3}$. Take the square root of $2^{2}$.
$$540\sqrt{7}\times 2\sqrt{3}$$
Multiply $540$ and $2$ to get $1080$.
$$1080\sqrt{7}\sqrt{3}$$
To multiply $\sqrt{7}$ and $\sqrt{3}$, multiply the numbers under the square root.
