Tentukan hasil penjumblahan bentuk aljabar

1) (6x+5)+(-3x-6)
= 6x-3x+5-6
= 3x-1
2) (6x-5y-2z)+(-8+6y+9z)
=6x-5y+6y-2z+9z
= 6x+y+7z
3)( 3(2x^2-4x+5)) + ( 2(4x^2+3x-7)
= ( 6x^2-12x+15) + ( 8x^2+6x-14)
= 6x^2+8x^2-12x+6x+15-14
= 14x^2-6x-1