\[\frac{4x - 25y}{2\sqrt{x} - 5\sqrt{y}} - 3\sqrt{y} =\]
\[= \frac{\left( 2\sqrt{x} - 5\sqrt{y} \right)\left( 2\sqrt{x} + 5\sqrt{y} \right)}{2\sqrt{x} - 5\sqrt{y}} - 3\sqrt{y} =\]
\[= 2\sqrt{x} + 5\sqrt{y} - 3\sqrt{y} =\]
\[= 2\sqrt{x} + 2\sqrt{y} = 2\left( \sqrt{x} + \sqrt{y} \right);\]
\[\sqrt{x} + \sqrt{y} = 4:\]
\[2 \cdot 4 = 8.\]