Question

Rocio leaves point A traveling due east at 40 miles per hour. At the same moment, Li leaves point A traveling due west at 50 miles per hour. After how many hours will they be 405 miles apart?)

Answer 1

Their speed of separation will be equal to the sum of their speeds because they are in opposite directions.
Speed of separation = 40 + 50 = 90 miles per hour

Time = distance / speed
Time = 405 / 90
Time = 4.5 hours