Please simply using long division: (-72 -4xsq +8xcu -36x) decided by (x-3). Thank you.

Answer 1

-72-4x^2+8x^3-36x
Geez, have you never noticed that polynomials are generally written in descending powers? Much preferred would be

8x^3-4x^2-36x-72

Using synthetic division, this is easy, or you can visit calc101.com, click on the long division button and then enter your polynomials.

Either way, you will find that you have a quotient of

4(2x^2+5x+6)