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 $2^{2}$.
$$E=2\sqrt{3}-\sqrt{3}+\sqrt{27}$$
Combine $2\sqrt{3}$ and $-\sqrt{3}$ to get $\sqrt{3}$.
$$E=\sqrt{3}+\sqrt{27}$$
Factor $27=3^{2}\times 3$. Rewrite the square root of the product $\sqrt{3^{2}\times 3}$ as the product of square roots $\sqrt{3^{2}}\sqrt{3}$. Take the square root of $3^{2}$.
$$E=\sqrt{3}+3\sqrt{3}$$
Combine $\sqrt{3}$ and $3\sqrt{3}$ to get $4\sqrt{3}$.
