The Displacement of a Vibrating String Versus Position Along the String

Multiple Choice

The displacement of a vibrating string versus position along the string is shown in the figure. The periodic waves have a speed of 10.0 cm/s. A and B are two points on the string.
-What is the wavelength of the wave?

A) 3.0 cm
B) 6.0 cm
C) 9.0 cm
D) 12 cm
E) 15 cm