Помогите пожалуйста!!! Очень срочно!!! Решите пример

Решите задачу:

$\displaystyle \bigg(\frac{\sqrt{n}}{\sqrt{m}+\sqrt{n}}- \frac{\sqrt{n}-\sqrt{m}}{\sqrt{n}} \bigg) : \frac{\sqrt{m}}{\sqrt{n}} = \\\\\\ = \frac{\sqrt{n} \cdot \sqrt{n}-(\sqrt{n}-\sqrt{m})(\sqrt{m}+\sqrt{n})}{(\sqrt{m}+\sqrt{n})\sqrt{n}} \cdot \frac{\sqrt{n}}{\sqrt{m}} =\frac{n-(n-m)}{(\sqrt{m}+\sqrt{n})\sqrt{m}} = \\\\\\ =\frac{m}{m+\sqrt{mn}} =\frac{m(m-\sqrt{mn})}{(m+\sqrt{mn})(m-\sqrt{mn})} = \frac{m(m-\sqrt{mn})}{m^2-mn} = \\\\\\ = \frac{m(m-\sqrt{mn})}{m(m-n)} =\frac{m-\sqrt{mn}}{m-n}$