Tolong jawab no.41 dan 42, please

42. diketahui : persamaan sistem linear
        2x -3y = a
       3x + y = -5a + b
     penyelesaiaan sisstem persamaaan tersebut (4,3)
 ditanya  nilai a + b = ....?
jawab
 (4,3)< ---->2x - 3y = a
              2.4 - 3.3 = a
                   8 - 9  =  a
                       - 1 = a
                         a = -1
(4,3) <-----> 3x + y = -5a + b
                   3.4 + 3 = -5a + b
                    12 + 3 = -5a + b
                          18 = -5a + b
subtitusi nilai a = -1 ke persamaan
<-->     18 = -5a + b
            18 = -5(-1) + b
            18 = 5 + b
             -b = 5 - 18
             -b = -13
              b = 13

nilai a + b = -1 + 13
                = 12