a) $$\frac{48}{42} = \frac{8}{7}$$
б) $$\frac{45 м}{54 м} = \frac{45}{54} = \frac{5}{6}$$
в) $$\frac{12 м}{2400 см} = \frac{12 \times 100 см}{2400 см} = \frac{1200}{2400} = \frac{1}{2}$$