A longitudinal standing wave is established in a tube open at only one end (see the drawing).

Question:

A longitudinal standing wave is established in a tube open at only one end (see the drawing). The frequency of the standing wave is 660 Hz, and the speed of sound in air is 343 m/s. What is the length of the tube?
(a) 0.13 m
(b) 0.26 m
(c) 0.39 m
(d) 0.52 m
(e) 0.65 m