A 20-M² Thermopane Window Is Constructed, Using Two Layers of Glass

A 2.0-m² Thermopane window is constructed, using two layers of glass 4.0 mm thick, separated by an air space of 5.0 mm. If the temperature difference is 20 $\degree$ C from the inside of the house to the outside air, what is the rate of heat flow through this window? (Thermal conductivity for glass is 0.84 W / m · $\degree$ C and for air 0.0234 W / m · $\degree$ C.)

A) 7700 W
B) 90 W
C) 180 W
D) 550 W