A hiker at the entrance to a cave yells to produce an echo. If the time between when the hiker yells, and when they hear the echo is 0.28 s, and the speed of sound at that
moment is 345 m/s, how deep is the cave

The boat's velocity relative to the riverbank can be resolved into two components. the component going north is 2.7 m/s and the component going west is 1.2 m/s.we add these two vectors and then find the magnitude of the resultant to get the speed.the magnitude of the resultant vector from adding can be obtained by the pythagorean theorem.    to two significant figures, the boat's speed relative to the riverbank is 3.0 m/s.