I have no clue how to do this (uniform motion

Question

1)2 bycicles start from the same point and ride in opposite directions. 1 rider is moving twice as fast as the other. In 3h, they are 72mi apart. Find the rate of each rider

Answer 1

Didn't each ride for 3 hours? (distance = time x rate)

so the slower went 3r mi
the faster went 3(2r) miles

so 3r + 6r = 72

solve for r