Q:  What is the total luminosity of this binary star?
           Express in terms of the solar luminosity, 3.8 x 10^(26) W


          L  =  4 pi RA^2 * sigma * TA^4  +  4 pi RB^2 * sigma * TB^4

             =  4 pi (9.04 x 10^(8) m)^2 * 5.67 x 10^(-8) J/K * (5810 K)^4

                 +  4 pi (5.56 x 10^(8) m)^2 * 5.67 x 10^(-8) J/K * (5030 K)^4

             =   6.63 x 10^(26) W  +  1.41 x 10^(26) W

             =   8.04 x 10^(26) W

             =   1.7 L(solar)      +  0.37 L(solar)

             =   2.1 L(solar)