3a+(2/3)b=c+7/3
c=3a+(2/3)b-7/3
2b-a/3=3-c
c=3-2b+a/3
3a+(2/3)b-7/3=3-2b+a/3 两边乘3
9a+2b-7=9-6b+a
9a-a+2b+6b=9+7
8a+8b=16
a+b=2