A vibrating string will be resonant at its fundamental frequency and all of its harmonics. Here's how it works:

* Fundamental Frequency: This is the lowest frequency at which the string can vibrate, which you've given as 30 Hz.

* Harmonics: These are multiples of the fundamental frequency.

So, the vibrating string will also be resonant at:

* 2nd harmonic: 30 Hz * 2 = 60 Hz

* 3rd harmonic: 30 Hz * 3 = 90 Hz

* 4th harmonic: 30 Hz * 4 = 120 Hz

* And so on...

In general, the resonant frequencies of a vibrating string are given by:

* f = n * f₀ where:

* f is the resonant frequency

* n is the harmonic number (1, 2, 3, ...)

* f₀ is the fundamental frequency