After a fire starts in a room, the walls are exposed to combustion products at 950C. If the interior wall surface is made of oak, how long after exposure to the fire will the wood surface reach its combustion temperature of 400C? Pertinent data are the following: h=30 w/m^2. k T(initial)=21.c for oak- P--545 kg/m^3 k=o.17 w/m.k Cp=2.385 kj/kg.k