Answer :
Given
Lenght 3m
Procedure
The relationships between the standing wave pattern for a given harmonic and the length-wavelength relationships for closed-end air columns are summarized below.
Harmonic # 3
[tex]\begin{gathered} \lambda=\frac{4}{3}\cdot L \\ \lambda=\frac{4}{3}\cdot3 \\ \lambda=4\text{ m} \end{gathered}[/tex]The second-longest wavelength would be 4m