And.. where is the rest of the question?
To solve this problem it is necessary to apply the concepts related to wavelength depending on the frequency and speed. Mathematically, the wavelength can be expressed as

Where,
v = Velocity
f = Frequency,
Our values are given as
L = 3.6m
v= 192m/s
f= 320Hz
Replacing we have that


The total number of 'wavelengths' that will be in the string will be subject to the total length over the size of each of these undulations, that is,



Therefore the number of wavelengths of the wave fit on the string is 6.
Take into account that in a standing wave, the frequency f of the points executing simple harmonic motion, is simply a multiple of the fundamental harmonic fo, that is:
f = n·fo
where n is an integer and fo is the first harmonic or fundamental.
fo is given by the length L of a string, in the following way:
fo = v/λ = v/(L/2) = 2v/L
becasue in the fundamental harmonic, the length of th string coincides with one hal of the wavelength of the wave.
The nail will have the ability to pull the pile of paperclips in a magnetic field. Meaning the nail will work as if it is a magnet