Two strings of lengths $L_{1}$ and $L_{2}$ are fixed at both ends. The wavespeed is the same for both strings. They both vibrate at the same frequency. $L_{1}$ vibrates at its first harmonic. $L_{2}$ vibrates at its third harmonic.

Two strings of lengths $L_{1}$ and $L_{2}$ are fixed at both ends. The wavespeed is the same for both strings. They both vibrate at the same frequency. $L_{1}$ vibrates at its first harmonic. $L_{2}$ vibrates at its third harmonic.

What is $\frac{L_{2}}{L_{1}}$ ?