Two rooms, each a cube 4.0m per side, share a 12-cm-thick brick wall. Because of a number

Question:

Two rooms, each a cube 4.0m per side, share a 12-cm-thick brick wall. Because of a number of 100-W lightbulbs in one room, the air is at 30oC, while in the other room it is at 10oC. How many of the 100-W bulbs are needed to maintain the temperature difference across the wall?