The velocity of the wave on the string is given by
[tex] v=\sqrt{\frac{T}{\frac{m}{L}}} \\
v=\sqrt{\frac{TL}{m}} [/tex]
Solving the above equation,
[tex] v^2=\frac{TL}{m} \\
L=\frac{v^2m}{T} [/tex]
The frequency of the wave [tex] f=300 [/tex] and wave length is [tex] 0.76 [/tex]
The velocity is [tex] v=(300)(0.76)=228 [/tex]
Substituting numerical values,
[tex] L=\frac{228^2(0.0059)}{200}\\
T=1.534 [/tex]
The length of the string is [tex] 1.534 m [/tex]