9514 1404 393
Answer:
5.29 mph
Step-by-step explanation:
The time is given by ...
time = distance/speed
Then the total time for the round trip, using x as the speed of the current, is ...
4/(6+x) +4/(6-x) = 6
where distances are in miles, time is in hours, and speed is in miles per hour.
Multiplying by the product of the denominators, we have ...
4(6 -x) +4(6 +x) = 6(6 -x)(6 +x)
48 = 6(36 -x^2)
x^2 = 28
x = √28 ≈ 5.29 . . . . miles per hour
The speed of the current was about 5.29 miles per hour.
_____
The trip upstream took about 5 hours and 39 minutes; the trip downstream took about 21 minutes.
