3x - y = 18
-y = 18 - 3x
y = -18 + 3x
5x + 2y = 8
5x + 2(-18 + 3x) = 8
5x - 36 + 6x = 8
5x + 6x = 8 + 36
11x = 44
x = 4
3x - y = 18
3(4) - y = 18
12 - y = 18
-y = 18 - 12
-y = 6
y = -6
Himpunan Penyelesaian = {x, y} = {a, b} = {4, -6}
a = 4
b = -6
2a + 3b = 2(4) + 3(-6)
= 8 - 18
= -10