$2.$ A rectangular fin has a thickness of $5$ mm$,$ a length of $0\mathrm{.}3$ m$,$ and a thermal conductivity of $60$ W$/$mK$.$ The fin is exposed to a fluid with a temperature of $80\backslash$deg C$,$ and its base temperature is $20\backslash$deg C$.$ Determine the heat transfer rate from the fin if the heat transfer coefficient is $20$ W$/$m$^2$K$.$