Раскроем скобки и упростим уравнение:
$$4x^2 - 12x + 9 - (x^2 - 25) = 4x + 14$$
$$4x^2 - 12x + 9 - x^2 + 25 = 4x + 14$$
$$3x^2 - 12x + 34 = 4x + 14$$
$$3x^2 - 16x + 20 = 0$$
$$D = b^2 - 4ac = (-16)^2 - 4 * 3 * 20 = 256 - 240 = 16$$
$$x_{1,2} = \frac{-b \pm \sqrt{D}}{2a} = \frac{16 \pm \sqrt{16}}{2 * 3} = \frac{16 \pm 4}{6}$$
$$x_1 = \frac{16 + 4}{6} = \frac{20}{6} = \frac{10}{3}$$
$$x_2 = \frac{16 - 4}{6} = \frac{12}{6} = 2$$
Ответ: $$x_1 = \frac{10}{3}$$, $$x_2 = 2$$