A red car is traveling 15 miles per hour faster than a blue car. if the red car travels 180 miles in the time needed for the blue car to travel 144 miles, find speed of each car

Their distance differs by 15 miles for each hour of travel time. Thus, the travel time of interest is

... (180 - 144) miles / (15 miles/hour) = 2.4 hour

The red car's speed is 180 mi / (2.4 h) = 75 mi/h.

The blue car's speed is 144 mi / (2.4 h) = 60 mi/h.