$$\frac{3\cdot4}{5\cdot8} = \frac{3\cdot4}{5\cdot2\cdot4} = \frac{3}{5\cdot2} = \frac{3}{10}$$
$$\frac{2\cdot6}{6\cdot9} = \frac{2\cdot6}{6\cdot3\cdot3} = \frac{2}{3\cdot3} = \frac{2}{9}$$
$$\frac{8\cdot9\cdot10}{9\cdot10\cdot16} = \frac{8\cdot9\cdot10}{9\cdot10\cdot2\cdot8} = \frac{1}{2}$$