Seconds would be the most likely answer.
The graph would be much much larger if it was in milliseconds, and much smaller in minutes and hours.
We calculate both velocities:
upstream 8 miles in 2 hours = 4 miles / hour
downstream 8 miles in 1 hour = 8 miles / hour
ps -stream speed = 4 mph
ps + stream speed = 8 mph
Adding both equations
2 ps = 12 mph
paddling speed = 6 mph
stream speed = 2 mph
7.6x = 64
7.6/7.6
Therfore, x = 64/7.16
x = 8.938
