A concrete wall is 15.0 cm thick and has an area of 10.0 m2. A layer of wood that is 2.50 cm thick is placed over the wall to reduce the loss of heat by thermal conduction. The thermal conductivity of concrete is 1.70 W/m °C and the thermal conductivity of wood is 0.0400 W/m °C. What is the effective thermal conductivity of the wood-on-concrete system?