A) When the train passes the roadside trees, the front of the train moves 1000m, and the speed is 1000m/4 min = 250m/min. When the train passes the bridge by the roadside, the front of the train moves (1000m+ bridge length). Time 12 minutes (1000m+ bridge length) = 12 minutes * vehicle speed (1000m+ bridge length) = 12 minutes * 250 m/min (/kloc- Car B leaves later than car A 10 minutes, and catches up with car A 40 minutes later. Car A meets car B, and car A moves (10+40) minutes * car A m/ min = 50 m car B moves for 40 minutes * car B m/ min = 40 m car A 50 a =40b = 1.25 car A starts 20 minutes later than car B, Car B starts later than car A 10 minutes. Car A moves (10+20+ 100) minutes *car A m/ min = 65438 car C moves 100 minutes * c m/min =/kloc. Caught up with b car x minutes after departure, When car B and car C met, car B moved for (20+x) minutes *b m/min = (20+x) * b m C car moved for x minutes * c m/min = x * c m (20+x) * b = x * c (20+x) *1.