Question

2 busses leave Houston at the same time and travel in opposite directions. 1 bus averages 55 miles per hour and the other bus averages 45 miles per hour. When will they be 400 miles apart?

Answer 1

Speed=distance/time  ⇒ distance=speed * time.
t=time when the busses are aparted 400 miles.
we can suggest this equation:
45 t+55 t=400
100t=400
t=400/100
t=4

Answer: the time will be 4 hours.