Question

Sound wave travel at 350 m/s through a warm air and at 3500 m/s through brass. The wavelength of a 700 Hz acoustic wave as it enters brass from warm air

Answer 1

velocity  v = f * λ
frequency f remains same in air or brass, for the acoustic waves.

In brass,  f = 700 Hz    v = 3500 m/s           wavelength = 3500/700=5 m
in air,  v = 350 m/s   wavelength = 350/700 = 1/2 meter

so wavelength becomes 10 times as waves enter brass from air.