Jawabanmu

2014-09-11T16:25:58+07:00
2014-09-11T16:30:24+07:00
(15a+7b-5c)-(-11a-12b+13d)
=15a+7b-5c+11a+12b-13d
=15a+11a+7b+12b-5c-13d
=26a+19b-5c-13d