(1) {2y-3x=6 => {2y-3x=6 => 2y+9-y=6 => y=-3
{y-3x=9 => {-3x=9-y => ----------- => -3x=9 - (-3) => x= -4
(x,y)=(-4; -3)
(2) {4x-5y=-22 => {4x-5y=-22 => 4(6 - 2/3 y) - 5y= -22 => y=6
3x+2y=18 => x=6 - 2/3 y => ------------ =>x=6- 2/3 *6 => x=2
(x,y)=(2,6)
(3) {5x+6y=0 => {5x+6y=0 => 5(4/3 - 4/3y)+6y=0 => y=10
3x+4y=4 => x=4/3 - 4/3y => ------------- => x=4/3 - 4/3*10 => x=-12
(x,y)=(-12,10)