P2

l = 4.3 m      V (wave speed) = 3.5 km/s      f = V/l = 3.5 x 10**3 / 4.3 = 814 Hz

P6

l = 2.25 m      f = 10 Hz,        V = 10 Hz x 2.25 m = 22.5 m/s    

P125

From (3) on the webpage: fo = fs (V + Vo) /(V + Vs)

Vo = 0,         Vs = 25 m/s,           fs = 500 Hz,         V = 334 m/s   sound speed

fo = 500 x 334 m/s  / (334 + 25) = 465 Hz