Consider a very long duct having the cross$-$section of an equilateral triangle. Each side of the triangle is $5$ cm $.$ One of the sides has emissivity of $0\mathrm{.}7$ and is at a temperature of $700$ K while another side is a black surface at temperature $400$ K $.$ The third side is insulated. $($i$)$ Draw the radiation exchange network for this configuration after necessary simplifications. $($ii$)$ Calculate the temperature of the insulated surface. Neglect end effects.