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 $3^{2}$.
Factor $48=4^{2}\times 3$. Rewrite the square root of the product $\sqrt{4^{2}\times 3}$ as the product of square roots $\sqrt{4^{2}}\sqrt{3}$. Take the square root of $4^{2}$.
$$2\sqrt{3}-\frac{3}{4}\times 4\sqrt{3}$$
Cancel out $4$ and $4$.
$$2\sqrt{3}-3\sqrt{3}$$
Combine $2\sqrt{3}$ and $-3\sqrt{3}$ to get $-\sqrt{3}$.
