The ends of a uniform metre stick of iron are maintained at $80^{\circ} \mathrm{C}$ and $30^{\circ} \mathrm{C}$. One end of another rod is maintained at $50^{\circ} \mathrm{C}$, where its other end should be touched on the metre stick so that there is no heat current in the rod in steady state?
(A) $40 \mathrm{~cm}$ from hot end
(B) $40 \mathrm{~cm}$ from cold end
(C) $50 \mathrm{~cm}$ from cold end
(D) $70 \mathrm{~cm}$ from cold end