x/3-y/4=1 ①
3x+2y=9 ②
①*12
4x-3y=12 ③
③*3
12x-9y=36 ④
②*4
12x+8y=36 ⑤
④-⑤
-17y=0
y=0
将y=0代入②
x=3
∴x=3 y=0