Simplify the expression: x(x+4) - 2(x-D)

Multiply $x$ by each term inside the first parenthesis, and multiply $-2$ by each term inside the second parenthesis.

$$x(x+4) - 2(x-D) = (x \cdot x) + (x \cdot 4) - (2 \cdot x) - (2 \cdot (-D))$$ $$= x^2 + 4x - 2x + 2D$$

Combine the terms with $x$.

$$x^2 + (4x - 2x) + 2D$$ $$= x^2 + 2x + 2D$$

The simplified expression is:

$$x^2 + 2x + 2D$$