A Periodic Transverse Wave Is Established on a String Such

Multiple Choice

A periodic transverse wave is established on a string such that there are exactly two cycles traveling along a 3.0-m section of the string. The crests move at 20.0 m/s.
-How long does it take a particle at the top of a crest to reach the bottom of an adjacent trough?

A) 0.018 s
B) 0.038 s
C) 0.075 s
D) 0.150 s
E) 0.30 s