Q$1($a$)$ The temperature at the inner and outer surfaces of a boiler wall made of $35mm$ thick steel and covered with an insulating material of $20mm$ thickness are $450C$ and $700C$ respectively. If the thermal conductivities of steel and insulating material are $78\frac{W}{m^0}C$ and $0\mathrm{.}156\frac{W}{m^0}C$ respectively, determine the rate of flow through the boiler wall.

$Q=\frac{(T)\text{o}\text{v}\text{e}\text{r}\text{a}\text{l}\text{l}}{Rth}$