18) 32a³ 18 / 9 12a² =

$$\frac{32a^3}{9} \cdot \frac{18}{12a^2} = \frac{32a^3 \cdot 18}{9 \cdot 12a^2} = \frac{32a \cdot 2}{1 \cdot 12} = \frac{8a \cdot 2}{1 \cdot 3} = \frac{16a}{3}$$