A bicycle racer is participating in a long-distance race. The racer has a strategy that involves maintaining different speeds during set intervals. For the first half of the race, the racer travels at a speed of 24 miles per hour (mph) for a distance of 60 miles.

After reaching the halfway point, the racer increases the speed to 36 mph for the next 90 miles.

What is the ratio of the time spent at the lower speed to the time spent at the higher speed? Express your answer in simplest form.