An electric hot plate is maintained at a temperature of 3500C, and is used to keep a solution boiling t 950C, and is used to keep a solution boiling at 950C. the solution is contained in cast iron vessel of wall thickness 25mm, which is enameled inside to a thickness of 0.8mm. the heat transfer coefficient for the boiling solution is 5.5 kW/m2K and the thermal conductivities of cast iron and enamel are 50 and 1.05W/mK, respectively. Calculate the OHTC and the rate of heat transfer per unit area