Q:  The apparent magnitude of a star is m = 18, while its apparent
          magnitude is M = 4.   What is the distance to the star?



              (m - M)  =  (18 - 4)  =   14   =  5 log(d) - 5


            ->    log(d)  =  ( 14 + 5 ) / 5  =  3.8

                           3.8
            ->    d   =  10      =  6,300 pc