How fast does train B need to travel to catch up?

Question

Train A leaves the station going west at 40 mph. 2 hours later train B heads west too. How fast does train B need to travel in order to catch up to train A in 6 hours?

Answer 1

If you mean "6 hours" is the time counting from when Train A left, then

A traveled 6 x 40mph = 240 miles. B travels 4 hours. Divide 4 into 240 to get 60 mph when B catches up.

If you mean "6 hours" is the time counting from when B left the station

then A traveled for 8 hours going 8 x 40 = 320 miles. B then would need to go 320/6 mph or 53 1/3 mph