Two plates A and B have thermal conductivities $84 \mathrm{Wm}^{-1} \mathrm{~K}^{-1}$ and $126 \mathrm{Wm}^{-1} \mathrm{~K}^{-1}$ respectively. They have same surface area and same thickness. They are placed in contact along their surfaces. If the temperatures of the outer surfaces of A and B are kept at 100 °C and 0 ºC respectively, then the temperature of the surface of contact in steady state is ________°C