Using the result of the previous exercise, calculate the skin depth = 1/k I for the penetration

Using the result of the previous exercise, calculate the skin depthλ = 1/k_I for the penetration of an electromagnetic wave into a metal surface, as a function of frequency and the material parameters n (the electron density), m (the electron mass) and τ (the average electron scattering time). For realistic parameters for a metal, that is, n = N/V = 10²¹ cm⁻³ and τ = 1 ps, what is the skin depth of a 10 MHz electromagnetic wave?