Three conductors of same length having thermal conductivity k ₁, k ₂ and k ₃ are connected as shown in figure. Area of cross sections of 1^ st and 2^ nd conductor are same and for 3^ rd conductor it is double of the 1^ st conductor. The temperatures are given in the figure. In steady state condition, the value of is _______ ^ C . (Given : k ₁=60 Js ⁻¹ ~m ⁻¹ ~K ⁻¹, k ₂=120 Js ⁻¹ ~m ⁻¹ ~K ⁻¹, k ₃=135 Js ⁻¹ ~m ⁻¹ ~K ⁻¹