ANSWER
3.28 m
EXPLANATION
The length of the string and the wavelength when the string is vibrating as its nth harmonic is related by,
[tex]L=\frac{n}{2}\cdot\lambda[/tex]In this problem, we are given the length of the string L = 8.2 m and we have to find the wavelength for this wave when the string is vibrating as the 5th harmonic,
[tex]8.2m=\frac{5}{2}\cdot\lambda[/tex]Solving for the wavelength λ,
[tex]\lambda=\frac{2}{5}\cdot8.2m=3.28m[/tex]The wavelength of this wave is 3.28 m.