Задание 273

$$\frac{\sqrt{7x+1}}{4}=2$$

$$\sqrt{7x+1}=2\cdot 4$$

$$\sqrt{7x+1}=8$$

$$(\sqrt{7x+1})^2=8^2$$

$$7x+1=64$$

$$7x=64-1$$

$$7x=63$$

$$x=9$$