Q:  Use the red line (RGB stars with age 13 Gyr and metallicity
           Z = 0.008) to estimate the apparent magnitude of the
           tip of the red giant branch in this galaxy.


                 m  =~  27


    Q:  ASSUMING that the stellar models are correct,
           how far away is this galaxy?


                (m - M)       =  5 log d  -  5

               (27 - (-4.2))  =  5 log d  -  5

                  31.2        =  5 log d  -  5


                           (31.2 + 5) / 5
                  d   =  10

                      =   17 Mpc   approx