We are given a closed air column and we are asked to determine the resonant frequencies. To determine the first frequency we will use the following formula:

Where:

Substituting we get:

Solving the operations we get:

Therefore, the first low frequency is 142 Hertz.
Now, to determine the second frequency we use the fact that a closed air column will produce odd harmonics only, therefore, the second frequency is determined by multiplying the first frequency by 3, like this:

Substituting we get:

Therefore, the second frequency is 426 Hz. Now, the third frequency is determined by multiplying the first frequency by 5:

Substituting we get:

Therefore, the third frequency is 710 Hertz.