\u59b9\u59b9\u548c\u54e5\u54e5\u4eca\u5e74\u7684\u5e74\u9f84\u548c\u662f30\u5c81\uff0c\u5f53\u54e5\u54e5\u662f\u59b9\u59b9\u73b0\u5728\u8fd9\u6837\u5927\u65f6\uff0c\u59b9\u59b9\u7684\u5e74\u9f84\u6070\u597d\u662f\u54e5\u54e5\u7684\u4e00\u534a

\u59b9\u59b9\u4eca\u5e74\u7684\u5e74\u9f84a\u54e5\u54e5\u4eca\u5e74\u7684\u5e74\u9f84b
a+b=30
a=2(a-(b-a))
\u5f97a=12
b=18
\u6240\u4ee5\u54e5\u54e5\u4eca\u5e7418\u5c81\u3002

x+y=30
y=2x

x+2x=30
\u59b9x =10 \u54e5y=20