7.5x=3.5y
15x=7y .1
5x+5y=40
15x+15y=120.2
将1式代入2式得
15y+7y=120
22y=120
11y=60
y=60/11
15x=7y
15x=7*60/11
x=7*4/11
x=28/11
所以x=28/11,y=60/11