composite wall consists of $15$ cm thick layer of material A and a $30$ cm thick layer of material B$.$ thermal conductivities of the two materials are unknown but constant. The outer surface temperature of the material A is $250\backslash$deg C and that of B is $50\backslash$deg C$.$ An insulation of k$=0\mathrm{.}05$ W$/$mK and thickness $2$ cm is added to the outer face of B$.$ It is observed that the outer surface of A acquires a temperature of $330\backslash$deg C and the junction between B and insulation is at $230\backslash$deg C$.$ The outer surface of the insulation is at $30\backslash$deg C$.$Estimate the rate of heat flow per m$?$ i$)$ before the addition of insulation, ii$)$ after the addition ofinsulation.