Not sure where to begin with this question--any help appreciated!

Question

Two kids sitting on opposite sides of a small lake use sticks to beat the surface of the
water at a frequency f=1.5 Hz. They notice that a standing wave pattern develops between
the points where they are disturbing the water surface. They count n=5 nodes over the
L=10 m distance between them.
What can be said about the speed of wave propagation on the water surface based on
this information.