The temperature at any point (x, y, z) of a cast-iron is given by T(x, y, z) = (x2 + y2)z. Compare the heat flows across the boundary of the four solid given below, by assuming that all are oriented outward and are built with the cast-iron with the thermal conductivity of 55. What are the minimum and maximum heat flows and why? (a) A cylinder given by inequalities x2 + y2 = 1,1 5z 4. (b) A sphere given by inequalities 0