Vsadnik 12km/ch (0km) , Peshexod 4km/ch (24km)
12 / 4 = 3
12 * 3 + 0 = 36km
4 * 3 + 24 = 36km
Vsadnik 3 raz bistree , i cherez 3ch budet 36km
Peshexod cherez 3ch budet 36km
36 - 24 = 12
Cherez 3ch , na 36km , znachit rostayanii 12km ot punkta B vsadnik dogonit peshexoda