Решим уравнение.
$$-x = 4 - 3(3x - 8)$$
$$-x = 4 - 9x + 24$$
$$-x + 9x = 28$$
$$8x = 28$$
$$x = \frac{28}{8} = \frac{7}{2} = 3.5$$
Ответ: 3.5