Jawabanmu

2014-02-11T19:35:14+07:00
3a + 7 = 31 - a
3a + a = 31 - 7
2a = 24
a = 12
2014-02-11T19:36:39+07:00
3a + 7 = 31 - a
3a = 31 - 7 - a
3a + a = 24
4a = 24
a = 24 : 4
a = 6