10) $$\frac{3x}{a-2} \cdot \frac{2-a}{9} = \frac{3x}{a-2} \cdot \frac{-(a-2)}{9} = -\frac{3x(a-2)}{9(a-2)} = -\frac{x}{3}$$
Ответ: $$- \frac{x}{3}$$