Jawabanmu

2014-09-11T13:38:59+07:00
(15a+7b-5c)-(-11a-12b+13d) = 15a+7b-5c+11a+12b-13d
                                               = 15a+11a+7b+12b-5c-13d
                                               = 26a+19b-5c-13d
2014-09-11T13:39:43+07:00
15a- (-11a) = 26a
7b - (12b)= 19b
-5c - 0= -5c
0-13d = -13d

*kalogslh