A salmon swims 15 miles downstream from its birth to the ocean in 3 hours. The return trip upstream to spawn takes 5 hours. How fast does the salmon swim in still water?

Answer 1

salmon's rate of swimming --- x mph
let rate of current be y mph
15/(x+y) = 3
3x+3y=15 ---> x+y=5

15/(x-y)=5
5x - 5y = 15 ----> x - y = 3

add those two equations:
2x = 8
x = 4 , then y = 1

state your conclusion