A section through a very long large sheet of metal 25 thickness and initially at uniform temperature T, is suddenly exposed on both sides to steam at Ts. At the start of heating, both side temperatures are quickly increased and subsequently held constant at temperature Ts. Consider a thin layer of thickness dx located at distance x from the left side of the sheet. The two sides of the sheet are isothermal surfaces. You may assume that the thermal resistance between the steam and the surfaces of the sheet is negligible. Under the conditions of constant thermophysical properties, no heat generation, thermal symmetry about the midplane, and uniform initial temperature, answer the following: a) Perform a heat energy balance of the sheet for the small-time interval dt to find the one-dimensional unsteady state heat conduction in the solid sheet. State which term(s) may be neglected or eliminated and why. b) Find the general differential equation