Решим уравнение:
$$\frac{x}{7}+\frac{x}{4} = -8$$
$$\frac{4x + 7x}{28} = -8$$
$$\frac{11x}{28} = -8$$
$$11x = -8 \times 28$$
$$11x = -224$$
$$x = -\frac{224}{11}$$.
Ответ: $$\frac{-224}{11}$$