1. The problem statement, all variables and given/known data Calculate the R-value of the stack of materials whose total thickness is made up of the individual thicknesses: material 1; k = 0.123 W/m/K, thickness = 0.103 m material 2: k = 0.234 W/m/K, thickness = 0.092 m material 3: k = 0.345 W/m/K, thickness = 0.081 m Hence calculate the heat flow per unit area through such a stack with has temperatures of 20 °C and -5 °C on opposite sides of the stack 2. Relevant equations R = ΔT/QA, Where QAis heat flux 3. The attempt at a solution I've no idea how to do this problem! Please help!