1. The problem statement, all variables and given/known data We have a wall of 30cm thickness, an inner surface temp of 500Kelvins and outer surfce temperature of 60Kelvins. 2. Relevant equations thermal conductivity = k(a) = 60 + 0.0006a^2, where a = temperature. fouriers law = q = -kA(da/dx) 3. The attempt at a solution What is the expression for da/dx and how would the rate of heat transfer be derived? I know there an inegration in there somewhere!! I'm completely stuck with this one so haven't even attempted to find a solution.