6n + 9 = -3n - 21 - 6.....simplify the right hand side
6n + 9 = -3n - 27 ....add 3n to both sides
6n + 9 + 3n = -3n + 3n - 27....simplify
9n + 9 = -27....subtract 9 from both sides
9n + 9 - 9 = -27 - 9...simplify
9n = - 36.....divide both sides by 9
(9/9)n = -36/9....simplify
1n or just n = - 4
