![http://calc101.com/webMathematica/
First step: Realize that xx needs to be multiplied by x^2x2 in order to be the x^3x3 in x^3-10x^2+30x+3x3−10x2+30x+3. Then, multiply the x^2x2 throughout x-5x−5 to get x^3-5x^2x3−5x2 and SUBTRACT it (remember, the signs will change) from x^3-10x^2+30x+3x3−10x2+30x+3.
You are left with -5x^2+30x+3−5x2+30x+3, but only the first term is important for now. Like you did with the x^3x3 in the first step, realize that you will need to add a -5x−5x on top so that the x(-5x)=-5x^2x(−5x)=−5x2. Continue multiplying and subtracting until you get to 28, which is the remainder.
All together, the answer would be written as:
color(blue)(x^2-5x+5+28/(x-5)x2−5x+5+28x−5