#"Since the wave crest labeled with Y is formed after 4 seconds"##" from X, X travels 6 cm in 4 seconds."#
#"The propagation speed of the waves can be found."#
#v=x/t=6/4=1.5 (cm)/s#
#"There are 5 wave crest between X and Y."#
#5*lambda=6#
#lambda=6/5=1.2 cm(" wavelength")#
#v=lambda/T#
#T=lambda/v#
#T=(1.2)/(1.5)=0.8 "sec( Period)"#