6x(x-3) - x(2-x)

To simplify the expression \( 6x(x-3) - x(2-x) \), follow these steps:

1. Distribute \( 6x \) in the first term: \[ 6x(x-3) = 6x^2 - 18x \]

2. Distribute \( -x \) in the second term: \[ -x(2-x) = -2x + x^2 \]

3. Now combine the results: \[ 6x^2 - 18x - 2x + x^2 = 6x^2 + x^2 - 18x - 2x \]

4. Combine the like terms: \[ (6x^2 + x^2) + (-18x - 2x) = 7x^2 - 20x \]

Thus, the simplified expression is: \[ \boxed{7x^2 - 20x} \]