I have the algebra problem:

If a boat goes downstream 72 miles in 3 hours and upstream 60 miles in 6 hours, the rate of

the river and the rate of the boat in still water respectively are ________?

a. 7 &16 mph

b. 7&17

c. 6 &17 mph

d. 6 &18

e. none

I know the forumla is r x t = d however i come up with 26 & 10

am i approaching this incorrectly?