The figure shows $($in cross section$)$ a wall consisting of four layers, with thermal conductivities $k_1=0\mathrm{.}0566\frac{W}{m}*K,k_3=0\mathrm{.}0416\frac{W}{m}*K$ and $k_4=0\mathrm{.}138\frac{W}{m}*K(k_2$ is unknown$).$ The layer thicknesses are $L_1=1\mathrm{.}42cm,L_3=2\mathrm{.}96cm$ and is unknown$).$ The known temperatures are $T_1=30\mathrm{.}7C,T_{12}=22\mathrm{.}8C$ and $T_4=-10\mathrm{.}1C.$ Energy transfer through the wall is steady. What is interface temperature $T_{34}?$

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