"Terrance trains at the rate of 6 miles every half an hour and Jesse trains at the rate of 2 miles every 15 minutes. How long will each person take to run of a total of 50 miles at the given rates?"
I will treat this as two problems: Terrance's case and Jesse's case.
Terrance's rate is (6/.5) mph, or 12 mph, and Jesse's is (2/0.25) mph, or 8 mph.
At this rate, Terrance can run 50 miles in how many hours? Divide 50 miles by 12 mph: (50/12) hours, or (25/6) hours, or 4 hours 10 minutes.
At his won rate, Jesse can run 50 miles in (50 mi) / 8mph hours,
which reduces to 25/4 hours, or 6 1/4 hours.