Imagine you are sitting on a surfboard in the ocean, waiting to catch a big wave. When the ocean is still, you are sitting at a point that would be the midpoint (the undisturbed position) of any waves that come your way. You look out to see and see a set of waves coming your way. What you see is actually a pattern of troughs followed be crests of the waves moving toward you and the shore. The distance between the crests is 5 meters. A crest passes you every 20 seconds. 
 Answer these questions: 
 a. What is the wavelength? 
 b. What is the frequency? 
 c. What is the wave velocity?