Please do not round the numbers

1)   λ = 24.7 cm,  2) f = 13.88 Hz, 3)  L = 117.3 cm

Explanation:

1) This is a resonance process, that is, the wave going downwards will interfere with the wave going upwards.

This is a tube with one end closed and the other open, at the closed end there is a node and at the open end a belly, so the resonances are

       L = λ / 4

       λ = 4L                     1st harmonic

       λ = 4L / 3                third harmonic

       λ = 4L / 5                fifth harmonic

       λ = 4L / n ’              n’ odd number   n ’= (2n +1)

the wavelength is requested for the eighth resonance n = 8, the corresponding prime number is

          n ’= 2 8 +1

          n ’= 17

we substitute

     λ = 4 105/17

     λ = 24.7 cm

2) the speed of the wave is related to the wavelength and frequency

          v =   λf

          f = v /λ

          f = 343 / 24.7

          f = 13.88 Hz

3) the next resonance occurs for n = 9, so the prime number is

         n ’= 2 9 +1

         n ’= 19

         L = n’ λ / 4

         L = 19 λ / 4  

We must suppose a value for the wavelength, if the wavelength is present in the tube and the length of the column increases, the resonance number increases

         L = 19 24.7/4

         L = 117.3 cm