谁帮我解三元一次方程组

4x+9y=12 (1)
3y-2z=1 (2)
7x+5z=19/4 (3)

(2)*3: 9y-6z=3 (4)
(1)-(4): 4x+6z=9 (5)
(3)*4: 28x+20z=19 (6)
(5)*7: 28x+42z=63 (7)
(7)-(6):22z=44
z=2

将z=2代入（2）得：y=5/3
将z=2代入（3）得：x=-3/4

4x+9y=12 ........(1)
3y-2z=1 ........(2)
7x+5z=19/4 .....(3)
(1)-3*(2):4x+6z=9...........(4)
(4)*7-(3)*4: 22z=44
z=2
代入(4):4x+6*2=9
4x=-3
x=-3/4
z=2代入(2):3y-2*2=1
y=5/3
解为:
x=-3/4
y=5/3
z=2