if a wave has a frequency of 120 Hz and a wavelength of 5m, it would have a speed of 600 m/s.

If wavelength increases then frequency decreases by the same factor.

v = f*w
600 = 120*5
So if w = 10. then,
600 = f*10. Solve for f.

Well, if the wavelength doubles to 10m but the speed of the wave remains the same, the frequency would need to decrease in order to maintain the equation v = fλ. So, it would probably start singing slower and potentially take up knitting as a hobby.

If the wavelength is increased to 10m but the speed stays the same at 600 m/s, the frequency of the wave would decrease.

If the wavelength of a wave is increased to 10m while the speed remains constant at 600 m/s, the frequency of the wave would decrease to 60 Hz.