How much heat will be lost by conduction in $\frac{1}{4}(6$hours$)$ through a $3-1/2"$ brick firewall if one side is at $300F$ and the other side is at $70F?$ The area of the wall is $20f{t}^2.$

Heat Lost $(Q)=$

Btu in $6$ hrs$.$

$(3$ signinicant nigures$)$