Jawabanmu

2014-02-24T20:01:24+07:00
-21
(bener gak)
klo gk bnr sorry
3x-12+5x+20 = 7x-21
8x+8 = 7x-21
8x-7x = -21-8
x = -29
2014-02-24T20:08:29+07:00
3x -12 + 5x + 20 = 7x -21
3x + 5x -12 + 20 = 7x -21
8x + 8 = 7x -21
8x + 8 - 8 = 7x -21 - 8
8x = 7x -29 
8x-7x = 7x-7x -29
x = -29