Answer:

Step-by-step explanation:

I think you forgot to mention Susan's current age if not:
x+5
x-4
6x
Answer:
let x=rate of the rowing team in still water
x+4=rate of the rowing team with current
x-4=rate of the rowing team against current
travel time=distance/rate
..
90%2F%28x%2B4%29=10%2F%28x-4%29
90x-360=10x+40
80x=400
x=5 rate of the rowing team in still water=5 mph