Question

I need a quick help please. Show your work, thanks!

Answer 1

Wavelength is related to period by the expression: 
Speed = Wavelength / Period


 f = 1/p 
v = fλ 
v = λ/p, where: 

v = speed, f = frequency, λ = wavelength, p = period 

p = v/λ, λ = 20 
p = v/20