Carrie walks at 3mph Crystal rides bike at 9mph carrie takes

Carrie walks at 3mph
Crystal rides bike at 9mph
carrie takes 20 minutes longer than Crystal to get to school.
They live the same distance from school.
What is the distance to school?
This is what I have, not making sense?
d=rxt
d= 3 x (t + 20)

Solution

you know the rates
the distances are equal
solve for the time and then substitute to find the distance
(remember: 20 min is 1/3 hr)

3(t + 1/3) = 9 (t) ___ 3t + 1 = 9t ___ 1 = 6t ___ 1/6 = t

substituting ___ d = 9(1/6) = 9/6 = 1.5 mi