Terrence trains at a rate of 6 miles every half hour:
(6 miles)/(1/2 hours) = 6/(1/2) mph = 6*2 mph = 12 mph
Jesse trains at a rate of 2 miles every 15 minutes:
(2 miles)/(15/60 hours) = 2/(1/4) mph = 2*4 mph = 8 mph
The unit rate for Terrence is 12 mph.
The unit rate for Jesse is 8 mph.
