7) 5/6 x = -15; 8) -2 5/6 x = 17/18; 9) 12x = 3.

Решение:

1. 7) \( \frac{5}{6}x = -15 \)
   \( x = -15 \cdot \frac{6}{5} \)
   \( x = -3 \cdot 6 \)
   \( x = -18 \)
2. 8) \( -2\frac{5}{6}x = \frac{17}{18} \)
   \( -\frac{17}{6}x = \frac{17}{18} \)
   \( x = \frac{17}{18} \cdot \left(-\frac{6}{17}\right) \)
   \( x = -\frac{6}{18} \)
   \( x = -\frac{1}{3} \)
3. 9) \( 12x = 3 \)
   \( x = \frac{3}{12} \)
   \( x = \frac{1}{4} \)

Ответ: 7) \( x = -18 \); 8) \( x = -\frac{1}{3} \); 9) \( x = \frac{1}{4} \).