Question

What is the wavelength of the sound wave that reaches your ear in a 20∘c room?

Answer 1

Missing text in the problem (found on internet):
"A 70 cm -long steel string with a linear density of 1.0 g/m is under 200 N tension. It is plucked and vibrates at its fundamental frequency"

Solution: 
The frequency of the sound wave along the string is given by
$f= \frac{1}{2L} \sqrt{ \frac{T}{\mu} }$
where L=70 cm=0.7 m is the length of the string, T=200 N its tension and $\mu = 1g/m =0.001 kg/m$ is the linear density. Using these values in the formula, we find
$f=319.4 Hz$