Diketahui sistem persamaan 4x + 3y =23 dan 5x – 7y = –25. Nilai –3x + 6y adalah ….

4x + 3y = 23    x5    = 20x + 15y = 115
5x - 7y = -25    x4    = 20x - 28y = -100 dikurangi    =      43y = 215  =    y=5


4x + 3y = 23
4x + 3(5) = 23
4x + 15 = 23
4x = 23 - 15
4x = 8
x = 2

-3x + 6y =
-3(2) + 6(5)
-6 + 30 = 24
semoga membantu maaf kalau salah

(1) 4x + 3y = 23  I x 5
(2) 5x - 7y = - 25   I x 4


20x + 15 y = 115
20x - 28y = - 100
______________-
          43y = 215
              y = 5

subtitusikan y=5 ke persamaan (1),
4x + (3.5) = 23
4x + 15 = 23
         4x = 23-15
         4x = 8
           x = 2

maka, nilai -3x+6y
= (-3 x 2) + (6 x 5)
= (-6) + 30 = 24