4) $$\frac{x}{4-\sqrt{3}} = \frac{x \cdot (4+\sqrt{3})}{(4-\sqrt{3}) \cdot (4+\sqrt{3})} = \frac{x(4+\sqrt{3})}{16-3} = \frac{x(4+\sqrt{3})}{13}$$
Ответ: $$\frac{x(4+\sqrt{3})}{13}$$