On a cold winter's day, it is 30°F outside. Yet, the temperature of the outside surface of the mechanical engineering building is just slightly warmer by 3°F. Assume that the thickness of the building wall is 12 in., its thermal conductivity is 0.4 Btu/h-ft-R, and the convective heat transfer coefficient between the outer wall surface and the ambient air is 6 Btu/h-ft2-R. What is the temperature (°F) on the inside wall of the building?