Ответ:

1. [tex]v_{I} = \frac{100m}{5s} = 20 m/s, v_{II} = \frac{100m}{20s} = 5 m/s[/tex]
2. [tex]s_{I} = 20 * t, s_{II} = 100 - 5 * t, s_{I} = s_{II} = > 20 * t = 100 - 5 * t = > t = 4c[/tex]
3. [tex]s_{mI} = 20 * 4 = 80m, s_{mII} = 5 * 4 = 20m[/tex]