Two trains leave the same city at the same time, one going east and the other going west. If one train is traveling at 65 mph and the other at 72 mph, how many hours will it take for them to be 822 miles apart?

Use the formula distance = rate × time for each train and add these values together so in which the distance equals 822 miles. For the ?rst train, d = 65t and for the second train d = 72t, where d is the distance and t is the time in hours. Add the distances and set them equal to 822: 65t + 72t = 822. Combine such as terms on the left side of the equation: 137t = 822; divide 137t/822 both sides of the equation through 137: 137/137 = 822/137. The variable is now alone: t = 6. In 6 hours, they will be 822 miles apart.