Jawabanmu

2014-09-11T15:55:08+07:00
15+7b-5c+(-11a-12b+13d) = 15+7b-5c-11a-12b+13d = -11a-5b-5c+13d+15
2014-09-11T15:57:15+07:00
15 + 7b - 12b - 5c - 11a + 13d
= -11a - 5b - 5c + 13d + 15