In Slippery Creek Janna can row 50 km downstream in 5 hours

In Slippery Creek, Janna can row 50 km downstream in 5 hours or she can row 25 km upstream in the same amount of time. Find the rate she rows in still water.

Let speed in still water = x km/hr
Let speed of river = y km/hr
speed with river is x+y
speed against river is x-y

with river:
x+y = 50/5
x+y = 10

against river:
x-y = 25/5
x-y = 5

so, add the 2 equations together: 2x = 15 --> x = 7.5 km/hr
and therefore from x+y=10, y = 2.5 km/hr