We've calculated absolute magnitudes. The Sun's B - V color is 0.65. The ranking is thus Star A, Sun, Star B. 2. Most of the visible energy is emitted at the shortest visible wavelengths, i.e. blue. The wavelengths of the peak are inversely proportional to temperature.
Energy is inversely proportional to wavelength.
Thus, peak photon energy is proportional to temperature. The peak photons from the star thus carry 3.18 times more energy than the peak photons from the sun. On the main sequence, hotter necessarily means more massive. Thus, the star has a larger mass than the Sun. Main sequence lifetime is inversely proportional to the third power of mass.