Missing text in the problem (found on internet):
"
A 70 cm -long steel string with a linear density of 1.0 g/m is under 200 N tension. It is plucked and vibrates at its fundamental frequency"
Solution:
The frequency of the sound wave along the string is given by

where L=70 cm=0.7 m is the length of the string, T=200 N its tension and
is the linear density. Using these values in the formula, we find
