4. Решите уравнения: x · 15 = 135; y : 9 = 17; 120 − a = 48.

1. \(x \cdot 15 = 135\)
   \(x = 135 : 15 = 9\).
2. \(y : 9 = 17\)
   \(y = 17 \cdot 9 = 153\).
3. \(120 - a = 48\)
   \(a = 120 - 48 = 72\).

Ответ: \(x = 9\), \(y = 153\), \(a = 72\).