To solve the problem, it is necessary to apply the concepts related to Faraday's law, for which the voltage induced on a body is defined as follows,
[tex]\epsilon = NA(cos\theta) (\frac{\Delta B}{\Delta t})[/tex]
Here,
N = Number of loops
A = Area
[tex]\Delta B[/tex] = Magnetic Field
[tex]\Delta t[/tex] = Time
[tex]\theta[/tex] = Angle between the magnetic field and the surface
Replacing,
[tex]A = \dfrac{\epsilon}{Ncos\theta (\frac{\Delta B}{\Delta t})}[/tex]
[tex]A = \dfrac{80.0mV}{(65)cos(30) (\frac{600\mu T-200\mu T}{0.4})}[/tex]
[tex]A = 1.42m^2[/tex]
Each side of the coil has a length of
[tex]d = \sqrt{A}[/tex]
Then the total length of the wire,
[tex]L = N(4d)[/tex]
[tex]L = 4N\sqrt{A}[/tex]
[tex]L = (4)(65)\sqrt{1.42}[/tex]
[tex]L = 308.95m[/tex]
Therefore the total length of the wire is 308.95m