Solve these using elimination.

1)
x = 5 - 9y
4x + 9y = -7

2)
3x = 5y - 9
2y = 3x + 3

3)
10x - 5 = 3y
2x - 3y = 1

4)
-6x - 4y = 10
-12x - y = 13

1) x+9y=5 equation 1
4x+9y=-7 equation 2
equation 1-equation 2
(x+9y)-(4x+9y)=5-(-7)
x+9y-4x-9y=12
-3x=12
x=-4
sub x=-4 into equation 1
-4+9y=-7
9y=-7+4
y=-1/3
2) 3x-5y=-9e1
2y-3x=3e2
e1+e2
(3x-5y)+(2y-3x)= -9+3
3x-5y+2y-3x=-6
-3y=6
y=-2
sub y =-2 into e1
3x-5(-2)=-9
3x=-9-10
x=19/3
=6 1/3