Solving distance rate and time

Question

A motorboat travels 120 kilometers in 4 hours going upstream. It travels 168 kilometers going down stream in the same amount of time. What is the rate of the current

Answer 1

120 = 4(r-s) = 4r - 4s

168 = 4(r+s) = 4r + 4s

288 = 8r

r = 288/8 = 36

120 = 144 - 4s

-24 = -4s

s=6

4*36 + 4*6 = 144 +24 = 168 <-- yes it checks

the speed of the boat is 36

the speed of the current is 6