A sound wave of the form s = sm cos (kx wt + ) travels at

Question:

A sound wave of the form s = sm cos (kx – wt + Φ) travels at 343 m/s through air in a long horizontal tube. At one instant, air molecule A at x = 2.000 m is at its maximum positive displacement of 6.00 nm and air molecule B at x = 2.070 m is at a positive displacement of 2.00 nm. All the molecules between A and B are at intermediate displacements. What is the frequency of the wave?