help

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? What was his average speed?

Let his speed for the remaining distance=S
1 mile / 12 + 1 mile /S =15 / 60 [1/4 of an hour]

Solve for S
S = 6 mph - his speed for the remaining distance
2 miles / (1/4) of an hour=2 x 4 =8 mph - his average speed.