Let s be the speed of the person's kayak in still water.
Given, speed of current = 2 mph
Upstream distance = 9 miles
Speed of the person upstream = s-2
Time traveled upstream = 9/s-2
Downstream distance = 13 miles
Speed of the person downstream = s+2
Time traveled downstream = 13/s+2
Given,
9/s-2 = 13/s+2
Cross-multiplying,
9*(s+2) = 13*(s-2)
9s + 18 = 13s - 26
Grouping like terms together,
13s-9s = 26+18
4s = 44
s = 11 mph
Speed of person's kayak in still water = 11 mph
