To divide -x^4+6x^3+8x+12 by x^2-3x+9,
as -x^4/x^2=-x^2.
Now -x^2xx(x^2-3x+9)=-x^4+3x^3-9x^2
Subtracting -x^4+3x^3-9x^2 from -x^4+6x^3+8x+12, we get
(-x^4+6x^3+8x+12)-(-x^4+3x^3-9x^2)=3x^3+9x^2+8x+12
Now in similar way 3x^3+9x^2+8x+12, x^2-3x+9 can go 3x times and remainder will be
3x^3+9x^2+8x+12-3x(x^2-3x+9)
= 3x^3+9x^2+8x+12-3x^3+9x^2-27x
= 18x^2-19x+12
Now in this, x^2-3x+9 goes 18 times and remainder is
18x^2-19x+12-18(x^2-3x+9)=-19x+54x+12-162=35x-150
Hence when we divide -x^4+6x^3+8x+12 by x^2-3x+9, the quotient is -x^2+3x+18 and remainder is 35x-150