Which of the law can be understood in terms of Stefan's law?

Two identical square rods of metal are welded end to end as shown in figure (a). Assume that $10 \mathrm{cal}$ of heat flows through the rods in $2 \min$. Now the rods are welded as shown in the figure, (b). The time it would take for $10 \mathrm{cal}$ to flow through the rods now, is

Three metal rods made of copper, aluminium and brass, each $20 \mathrm{cm}$ long and $4 \mathrm{cm}$ in diameter, are placed end to end with aluminium between the other two. The free ends of copper and brass are maintained at $100$ and $0°\mathrm{C}$ respectively. Assume that the thermal conductivity of copper is twice that of aluminium and four times that of brass. The approximate equilibrium temperatures of the copper aluminium and aluminium-brass junctions are respectively-

A closed cubical box is made of a perfectly insulating material walls of thickness $8 \mathrm{cm}$ and the only way for heat to enter or leave the box is through two solid metallic cylindrical plugs, each of cross-sectional area $12 {\mathrm{cm}}^2$ and length $8 \mathrm{cm}$, fixed in the opposite walls of the box. The outer surface $A$ on one plug is maintained at $100°\mathrm{C}$ while the outer surface $B$ of the other plug is maintained at $4°\mathrm{C}$. The thermal conductivity of the material of each plug is $0.5 \mathrm{cal} °{\mathrm{C}}^{-1} {\mathrm{cm}}^{-1}$. A source of energy generating $36 \mathrm{cal} {\mathrm{s}}^{-1}$ is enclosed inside the box. Assuming the temperature to be the same at all points on the inner surface, the equilibrium temperature of the inner surface of the box is