(1.18) A storage tank to be used in a chemical process is spherical in shape and is covered with a 3-in. thick layer of insulation having anR-value of 12. The tank will hold a chemical intermediate that must be maintained at 150F. A heating unit is required to maintain this temperature in the tank. (a) What is the thermal conductivity of the insulation? (b) Determine the duty for the heating unit assuming as a worst-case scenario that the exterior surface of the insulation reaches a temperature of 20F. (c) What thermal resistances were neglected in your calculation? Ans. (a) k = 0.02083Btu/h ft F. (b) q = 7900 Btu/h. help me this question