\[\frac{\sqrt{x} - 6}{\sqrt{x}}\ :\frac{x - 36}{4x} =\]
\[= \frac{\left( \sqrt{x} - 6 \right) \cdot 4x}{\sqrt{x} \cdot (x - 36)} =\]
\[= \frac{4\sqrt{x}}{\sqrt{x} + 6}\]