$8\mathrm{.}31$ A plane wave in air with E$=(89+$y$84-6)$e j$(2$r$+33)($Im$)$ is incident upon the planar surface of a dielectric material, with & $=2\mathrm{.}25,$ and it occupies the half$-$space $<20.$ Determine: $($b$)$ the frequency of the wave, $($c$)$ the field Er of the reflected wave, $($d$)$ the field E$\text{'}$ of the wave transmitted into the dielectric medium, and $($e$)$ the average power density carried by the wave into the dielectric medium $*($a$)$ the incidence angle $,$