$4.$ A finned heat sink is used to cool an electronic component. The heat sink has a base area of $0\mathrm{.}02$ m$^2,$ and its thermal conductivity is $200$ W$/$mK$.$ The base temperature of the heat sink is maintained at $80\backslash$deg C$,$ while the ambient temperature is $20\backslash$deg C$.$ The fin thickness is $2$ mm$,$ and the fin height is $10$ mm$.$ The fin is made of aluminum with a thermal conductivity of $220$ W$/$mK$.$ Calculate the heat transfer rate from the heat sink, and the fin efficiency.