-9x^3-72x^2+36=3x^3+x^2-3x+8 Add 9x^3 to both sides.
-72x^2 + 36 = 3x^3 + 9x^3 + x^2 - 3x + 8 Add 72x^2 to both sides
36 = 12x^3 + 73x^2 - 3x + 8 Subtract 36 from both sides.
0 = 12x^3 + 73x^2 - 3x - 28
It does factor, but it is not very nice.
(x + 6.06)(x - 6.09)(x + 0.632)
If there is any kind of error please report it in a note below.

First, you need to find where you can move the decimal point to so that there is only one non-zero digit to the left of it.
Move the decimal point, and that is the first part done.
Add "
".
For the last part - the power, you need to find how many decimal places you moved the decimal point. In this case, we moved it to the right 2 places, so the power is
.
If, for example, we had moved the decimal point three places to the left, the power would be
.
So,
0.2(n - 6) = 2.8
Distribute.
0.2n - 1.2 = 2.8
Add 1.2 to both sides.
0.2n = 4
Divide both sides by .2.
n = 20
Check.
0.2(20 - 6) = 2.8
Simplify inside parentheses.
0.2(14) = 2.8
Multiply.
2.8 = 2.8 This checks.
S = {2.8}
Do you have a picture to go with it?