Heat is lost through a plane wall steadily at a rate of $800 \mathrm{~W}$. If the inner and outer surface temperatures of the wall are $20^{\circ} \mathrm{C}$ and $9^{\circ} \mathrm{C}$, respectively, and the environment temperature is $0^{\circ} \mathrm{C}$, the rate of exergy destruction within the wall is
$(a) 0 \mathrm{~W}$
(b) $11 \mathrm{~W}$
(c) $15 \mathrm{~W}$
$(d) 29 \mathrm{~W}$
(e) $76 \mathrm{~W}$