For plane walls at steady$-$state without internal generation, we can bypass

equation $2\mathrm{.}24.$ A shown in class

the temperature distribution is always linear

the flux is the same at every point in the wall

we can just use equation $1\mathrm{.}3,$ often expressed as $q_k=k(Delta\frac{T}{\frac{?}{?}}L).$ The

term $\frac{T}{L}$ is the wall temperature gradient.