Yuto left his house for bike ride at 10am. when riko left yuto was 5.25 miles along path. if yutos average speed was 0.25 mpm and rikos was 0.35mpm , over what time period in minutes, t, strting from when riko left will riko be behind yuto

-- When Riko left the house, Yuto was 5.25 miles ahead of her.

-- From the time she left the house, she gained (0.35 - 0.25) = 0.1 mile on Yuto
every minute ... closing the gap at the rate of 0.1 mile per minute.

-- If she can keep it up, she'll close the gap in (5.25 / 0.1) = 52.5 minutes.

-- Riko is behind her brother when  0 ≤ t < 52.5 minutes .

The answer would be 315 because you need to subtract