One side of a copper block 4 cm thick is maintained at 175C. The other side is

Question:

One side of a copper block 4 cm thick is maintained at 175ºC. The other side is covered with a layer of fiberglass 1.5 cm thick. The outside of the fiberglass is maintained at 80ºC, and the total heat flow through the composite slab is 300 W. What is the area of the slab?