2. The insulation boards for air-conditioning purposes are made of three layers, middle one is being of packed grass of 10 cm thick (k=0.02 W/mC) and the sides are made of plywood each of 2 cm thick (k=0.12 W/mC). They are glued with each other. Determine the (a) heat flow rate per m if one surface is at 35C and the other surface is at 20C. (b) Instead of glue, if these three pieces are bolted by one central bolt of 1 cm diameter (k= 40 W/mC) per m of the board then find the heat flow rate m of the combined board. per 7