Two spheres of same material and radius $r$ and $2r$ are heated to same temperature and are kept in identical surroundings, ratio of their rate of loss of heat is

If a graph is plotted by taking spectral emissive power along $y$-axis and wavelength along $x$-axis then the area below the graph above wavelength axis is

Three rods of same material, same area of cross-section but different lengths $10 \mathrm{cm}, 20 \mathrm{cm}$ and $30 \mathrm{cm}$ are connected at a point as shown. What is temperature of junction $O?$