Answer: the speed at which Jonathon and Samantha can row in still water is 9 mph
Step-by-step explanation:
Let x represent the speed of the canoe in still water.
Let y represent the speed of the river's current.
Jonathon and Samantha row their canoe 28 miles downstream in 2 hours. Assuming they rowed with the current, the total speed would be (x + y) mph
Distance = speed × time
Distance travelled downstream is expressed as
28 = 2(x + y)
Dividing through by 2, it becomes
14 = x + y - - - - - - - -1
After a picnic, they row back upstream. After 3 hours they only travel 12 miles. Assuming they rowed against the current, the total speed would be (x - y) mph
Distance travelled upstream is expressed as
12 = 3(x - y)
Dividing through by 3, it becomes
4 = x - y - - - - - - - -2
Adding equation 1 and equation 2, it becomes
18 = 2y
y = 18/2
y = 9 mph
