The electric field of a uniform plane wave propagating in lossless isotropic medium is E(x,t) = 60π cos(3*108 t + 4x) αy V/m. The magnetic field at point (0,0,0) when t = 0 is 1A/m. The unit of t is second and the unit of x is meter. Find:
(1) the phase velocity vp;
(2) the wave impedance n of the media;
(3) the relative dielectric constant εr and relative permeability μr;
(4) the time domain expression for magnetic field;