(12 + 7x) * 2 = 24

Решение:

1. \( (12 + 7x) \cdot 2 = 24 \)
2. \( 12 + 7x = \frac{24}{2} \)
3. \( 12 + 7x = 12 \)
4. \( 7x = 12 - 12 \)
5. \( 7x = 0 \)
6. \( x = \frac{0}{7} \)
7. \( x = 0 \)

Ответ: 0