To simplify this expression, we need to first find common denominators and combine like terms.

Given expression:

(36/x^2 - 9) - (x - 3/x) - (3x/3 - x) / (6/(3-x))

First, simplify the fractions inside the parentheses:

= (36/x^2 - 9) - (x^2 - 3) - (x) / (3)

Next, find common denominators and combine like terms:

= (36 - 9x^2) / x^2 - (4x + 3) / 3

Now, move the second fraction to the numerator:

= (36 - 9x^2 - (4x + 3)x^2) / (3x^2)

= (36 - 9x^2 - 4x^3 - 3x^2) / (3x^2)

= (36 - 12x^2 - 4x^3) / (3x^2)

= (-4x^3 - 12x^2 + 36) / (3x^2)

Therefore, the simplified expression is (-4x^3 - 12x^2 + 36) / 3x^2.