Hi! Could you help me with this question?
imgur(dot)com/lJk2Mfa(dot)png
2 answers
https://webhome.phy.duke.edu/~rgb/Class/phy51/phy51/node49.html
For relation between wave phase speed and frequency and length
https://webhome.phy.duke.edu/~rgb/Class/phy51/phy51/node47.html
https://webhome.phy.duke.edu/~rgb/Class/phy51/phy51/node47.html