Jawabanmu

2014-05-29T15:45:25+07:00
= 14 . ( 7000 - 6800)
= 14 . 200
= 2800
2014-05-29T15:51:05+07:00
Rata-rata = {(14x7000) + (1xa)} / (14+1)
6800 = (98000+a) / 15
98000+a = 102.000
a = 4000