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
 is the linear density. Using these values in the formula, we find
