Ling lives 2 miles from school. It took him 15 minutes to bike from school to home. The first half of the distance he biked at a speed of 12 mph. What was his speed for the remaining distance

As we know that

time = distance/speed

The time used for firs half of the trip was

(1 mi) (12 mi/hour) = 1/12 hours = 5 minutes

The last half of the trip will took 10 minutes, 1/6 hour.

Speed = distance / time

(1 mil) = (1/6h) = 6 mil/h

so the speed for last half of the trip was = 6mph

the average speed was

(2mil) (1/4 hour) = 8 mil/hour

So the ling's average speed was 8mph.