Answer
d) $1.5\frac{W}{m^2*^{\circ}C}$
Work Step by Step
First we calculate the area of the wall:
$A=8m*4m=32m^2$
Knowing that the heat transfer in this case is by conduction:
$Q_{cond}=\frac{kA\Delta T}{L}$
$k=\frac{Q_{cond}L}{A\Delta T}=\frac{2400W*0.2m}{32m^2*(15^{\circ}C-5^{\circ}C)}=1.5\frac{W}{m^2*^{\circ}C}$
