Look at the second part of the description first.
rate time distance
DOWN r+c t 5
UP r-c t 3
Really want a relationship between r and c.
or
Now analyze the first part of the description.
DOWN r+c () 20
UP r-c () 20
TOTAL 8 40
We can begin filling the two missing time cells.
DOWN r+c 20/(r+c) 20
UP r-c 20/(r-c) 20
TOTAL 8 40
The time-sum equation should be obvious:
.
Try simplifying this equation before substituting either for r or for c.
I have not finished this but you should be able to.