Question 9349
If the child leaves at 1:00 p.m., then at 3:00 p.m. he will have gone 6 miles.
If the rafter leaves at 2:00 p.m., then at 3:00 he will have gone 9 miles.

The rafter would pass the child in his first hour of paddling.  At 2:30 p.m.
they would be at the same point.  Draw out a simple line graph to plot both
of their courses.  My drawing below doesn't line up right on my edit screen, but the 4.5
distances should line up:

Child          0           3       4.5         6

rafter                      0       4.5         9