(63 - 9x) : 3 = 15

Решение:

1. \( (63 - 9x) : 3 = 15 \)
2. \( 63 - 9x = 15 \cdot 3 \)
3. \( 63 - 9x = 45 \)
4. \( 63 - 45 = 9x \)
5. \( 18 = 9x \)
6. \( x = \frac{18}{9} \)
7. \( x = 2 \)

Ответ: 2