Question 387964
train A has a 12 min (6:22 - 6:10) head start , or 1/5 hr (12 / 60)


at 100 mph , 1/5 hr means a 20 mi head start (100 mph * 1/5 hr)


train B is catching up at 25 mph (125 mph - 100 mph)


it takes train B 4/5 hr to catch up (20 mi / 25 mph) , this is 48 min (4/5 * 60)


so B catches A at 7:10 (6:22 + 0:48)