Perform the following operations :

a$.)$ Express your final answer in rectangular form :$(6-$ j $7)(4+$ j$2)=$

b$.)$ Express your final answer in polar form :

$6\mathrm{.}31-$ j $8\mathrm{.}23+(7\mathrm{.}14<23\mathrm{.}1$ degrees$)(-8\mathrm{.}92<-47\mathrm{.}5$ degrees$)$