Follow the derivation for the Fresnel equations in Griffith’s filling in any missing steps. This is page 405-409 of the US printed 4th edition. Comment on Brewster’s angle.
Now, show rederive the Fresnel equations for the case where the polarization of the electric field is perpendicular to the plane of incidence. That is, the wave fronts still come in at an angle as Fig. 9.15 shows, but the electric field is no longer in the $xz$ plane, it points in the $y$ direction. Do you find a Brewster’s angle?