$1.$The temperature at the inner and outer surfoces of a boiler wall mede of $20$ mm thick steel and covered with an insutsaing material of $5$ mm thickness are $300C$ and $50C$ respectively. If the thermal condectivities of steel and insultating material core $58\frac{k}{m}C$ and $0\mathrm{.}116l\frac{d}{m}C$ respectively. devermine the rate of flow through the boller well.