a) 8x + 7x = 1515
15x = 1515
$$x = \frac{1515}{15}$$
$$x = 101$$
Ответ: x = 101
б) 8 × (2x - 6) = 128
2x - 6 = 128 : 8
2x - 6 = 16
2x = 16 + 6
2x = 22
$$x = \frac{22}{2}$$
x = 11
Ответ: x = 11