x^2+3x-1=0 x^2+3x=1
x^3+5x^2+5x+18
=x^3+3x^2-x+2x^2+6x+18
=x(x^2+3x-1)+2x^2+6x+18
=2x^2+6x+18
=2(x^2+3x)+18
=2+18=20