Explanation:
1) Your problem → (4x^2 - 17x^3 + 9) - (x^2 + 9x + 23x^2 + 11)
(-17x^3+4x^2+9)-(x^2+23x^2+9x+11)
=-17x^3+4x^2+9-x^2-23x^2-9x-11
=-17x^3+4x^2-x^2-23x^2-9x+9-11
=-17x^3-20x^2-9x-2
2) Your problem → 0 - 19.73 - 25x^2 - 12x - 3
=0-19.73-25x2-12x-3
=-25x^2-12x-22.73
3) - 10.x^3 – 162x^2 – 24x - 4
4) Your problem → 17x^3 - 20x^2 - 9x^2
=17x^3-20x^2-9x^2
=17x^3-29x^2
5) -16x^3 – 243x^2 – 12x – 3