Answer:
7 mph
Step-by-step explanation:
Let x mph be the canoeist's rate in still water.
The speed of the current in a stream is 2 mph, then
- the canoeist's rate upstream is x-2 mph;
- the canoeist's rate downstream is x+2 mph.
The distance covered is 22.5 miles.
The time to go upstream
hours.
The time to go downstream
hours.
It takes a canoeist 120 minutes (= 2 hours) longer to paddle 22.5 miles upstream than to paddle the same distance downstream, then

The canoeist's rate cannot be negative, then his rate in still water is 7 mph.