A person hears sounds with a frequency in the range of about 16 Hz to 20000 Hz. What is the wavelength of sound in air and water corresponding to these frequencies? Please let me know the answer and how you got the answer (what formula you used)

Starting with only the balmer series light (visible light), how could we ensure that the solar panels generate a current that mark can use for his power station? a)by gradually increasing the brightness (amount) of light that we shine on it. b)by gradually increasing the frequency of the light we shine on it. c)by gradually increasing the wavelength of the light that we shine on it.