Minimum thickness of the wall required to prevent condensation - GATE ME '07

The building has to be maintained at 21 C (dry bulb) and 14.5 C (wet bulb). The dew point temp under these conditions is 10.17 C. The outside temp is −23 C (dry bulb) and internal and external surface heat transfer coefficients are 8 W/m^2.K and 23 W/m^2.K respectively. If the building wall has a thermal conductivity of 1.2 W/m.K, the minimum thickness (m) of the wall required to prevent condensation is A. 0.471 B. 0.407 C. 0.321 D. 0.125