The amplitudes of an elliptically polarized plane wave

The amplitudes of an elliptically polarized plane wave traveling in a lossless, nonmagnetic medium with r = 4 are Hy0 = 3 (mA/m) and Hz0 = 4 (mA/m). Determine the average power flowing through an aperture in the y-z plane if its area is 20 m2.