Three metal rods made of copper, brass and steel each of area of cross-section $4 \mathrm{~cm}^2$ are joined as shown in the figure. Their lengths are respectively $46 \mathrm{~cm}, 13 \mathrm{~cm}$ and $12 \mathrm{~cm}$. Their coefficients of thermal conductivity are respectively $0.92,0.26$ and 0.12 , all in CGS units. The rods are thermally insulated from the surroundings except at the ends. Rate of flow of heat through the copper rod, in cal s ${ }^{-1}$ is