An oven wall consist of a 0.25in thick layer of steel (Ks= 8.7 Btu/h x ft x degreeR) and a layer of brick (Kb = 0.42 Btu/h x ft x degreeR). At a steady state a temperature decrease of 1.2 degreeF occurs over the steel layer . The inner temperature of the steel layer is 540 degreeF. If the temperature of the outer surface of the brick must be no greater than 105 degreeF, Determine the minimum thickness of brick, in in., that ensures the limit is met?