令a=x+y,b=x-y
则a/5+b/7=2 (1)
3a+b/7=16 (2)
(2)-(1)
14a/5=14
a=5
b=7(16-3a)=7
x+y=5
x-y=7
相加
2x=12
x=6
y=5-x=-1