Let's list some variables:
v: speed of sound in air at 20ºC; v = 343 m/s
Since the first sound is heard when the air column is 9cm long, the wavelength of the wave is 4 times that, so 36cm. (λ1 = 4*L = 4*9)
λ: wavelength of sound; λ = 36cm
L: length of air column
We can use the following equations for the lengths of the air column for the second and third resonances, respectively:
λ = 4L/3
λ = 4L/5
Now let's plug in the value for the wavelength of sound, λ.
36 = 4L/3
L = 27cm (second resonance)
36 = 4L/5
L = 45cm (third resonance)
Answer: 0.27m and 0.45m