method of elimination~20points

1.
1.25y-0.75z=1 => 5y-3z-4=0 ---(1)
0.25y+1.25z=17 => y+5z-68=0 ---(2)
(1)x5+(2)x3:
5(5y-3z-4)+3(y+5z-68)=0
28y-224=0
y=8 ---(3)

Sub. (3) into (1):
5(8)-3z-4=0
3z=36
z=12

2.
3c+2d+4=0 ---(1)
2c-3d+7=0 ---(2)

(1)x3+(2)x2:
3(3c+2d+4)+2(2c-3d+7)=0
13c+26=0
c=-2 ---(3)
Sub. (3) into (1):
3(-2)+2d+4=0
2d=2
d=1

3.
5x=2x-2y+13 => 3x+2y-13=0 ---(1)
5x=3y+9 => 5x-3y-9=0 ---(2)

(1)x3+(2)x2:
3(3x+2y-13)+2(5x-3y-9)=0
19x-57=0
x=3 ---(3)
Sub. (3) into (1):
3(3)+2y-13=0
2y=4
y=2