19) 10 6x x / x³ 25 9 =

$$\frac{10}{x^3} \cdot \frac{6x}{25} \cdot \frac{x}{9} = \frac{10 \cdot 6x \cdot x}{x^3 \cdot 25 \cdot 9} = \frac{60x^2}{225x^3} = \frac{4}{15x}$$