diketahui persamaan 2x-5y+12=12 dan 5x-5y+9=0. nilai dari 3x-4y adalah?

2x -5y +12 = 0
5x -5y +9 = 0
-------------------- -
-3x + 3 = 0
-3x = -3
x = 1
5x - 5y +9 = 0
5.1 -5y + 9 = 0
5 - 5y + 9 = 0
5y = 14
y = 14/5
3x - 4y = 3.1 -4.14/5
= 3 - 56/5
= 15/5 - 56/5
= -41/5
= -8 1/5