\[\sqrt{27} - \sqrt{12} + \sqrt{75} =\]
\[= \sqrt{9 \cdot 3} - \sqrt{4 \cdot 3} + \sqrt{25 \cdot 3} =\]
\[= 3\sqrt{3} - 2\sqrt{3} + 5\sqrt{3} = 7\sqrt{3}.\]