-6 = 3x - 6y
4x = 4 + 5y
ok
x = (4 + 5y)/4
Substitution
-6 = 3[(4 + 5y)/4] - 6y
-6 = [12 + 15y]/4 - 6y
-6 + 6y = [12 + 15y]/4
-24 + 24y = 12 + 15y
24y - 15y = 12 + 24
9y = 36
y = 36/9
y = 4
x = (4 + 5(4))/4
x = [4 + 20)/4
x = 24/4
x = 6
Solution x = 6, y = 4