4x+9y=12 (1)
3y-2z-1=0 (2)
7x+5z=4又3/4 (3)
(1)-(2)×3
4x+6z=9 (4)
(3)×6-(4)×5
42x-30x=57/2-45
12x=-33/2
x=-11/8
y=(12-4x)/9=19/6
z=(19/4-7x)/5=23/8