The Longitudinal Displacement of a Mass Element in a Medium

Multiple Choice

The longitudinal displacement of a mass element in a medium as a sound wave passes through it is given by s = s_m cos (kx - ωt) .Consider a sound wave of frequency 440 Hz and wavelength 0.75m.If s_m = 12 µm, what is the displacement of an element of air located at x = 1.2 m at time t = 0.11 s?

A) 3.7 µm
B) 4.9 µm
C) 6.0 µm
D) 8.2 µm
E) 12 µm