The composite wall consists of three materials with area is $1m^2,$ two of which are of known thermal conductivity, $k_A=20\frac{W}{m}.C$ and $k_c=50\frac{W}{m}.C,$ and known thickness, $L_A=0\mathrm{.}3m$ and $L_C=0\mathrm{.}15m.$ The third material, B$,$ which is sandwiched between material A and C$,$ is of known thickness, $L_B=0\mathrm{.}15m,$ but unknown thermal conductivity $k_B.$ Under steady$-$ state operating conditions, measurements reveal an outer surface temperature of $T_{s0}=20C,$ an inner surface temperature of $T_{3,1}=600C,$ the equivalent thermal resistance of the wall is $0\mathrm{.}024\frac{C}{W}.$

Answer the following questions below

Q$18)$ What is the heat transfer rate through the wall in $($kW$)?$

A$)19\mathrm{.}64$

B$)21\mathrm{.}54$

C$)24\mathrm{.}17$

D$)22\mathrm{.}49$

E$)$ None of them.

Q$19)$ What is the thermal conductivity of material B in $(\frac{W}{m}*C)?$

A$)25\mathrm{.}0$

C$)18\mathrm{.}75$

B$)23\mathrm{.}18$

E$)$ None of them.

D$)15\mathrm{.}48$

Q$20)$ What is the temperature between material A&B in $(C)?$

A$)276\mathrm{.}9$

B$)237\mathrm{.}45$

C$)245\mathrm{.}15$

D$)200\mathrm{.}5$

E$)$ None of them.