Naoki bikes the 36 mi to Hillsboro averaging a certain speed. The return trip is made at a speed 3 mph slower.Total time for the round trip is 7 hr.Find Naoki's average speed on each part of the trip.

I set up a table.

Trip 1: Distance = 36 Speed = r Time = ???

Trip 2: Distance = 36 Speed = r-3 Time = ???

What do I set time as? x divided by 7? ?