Let's simplify the expression $X + x - 3 + 2(x - 3)$.

1. Distribute the 2 across the $(x - 3)$: $2(x - 3) = 2x - 6$ Now the expression becomes: $X + x - 3 + 2x - 6$

2. Combine like terms: $X + (x + 2x) - (3 + 6)$ This simplifies to: $X + 3x - 9$

So, the simplified expression is: $X + 3x - 9$

Would you like more details on any part of this?

Here are some related questions:

1. What happens if you substitute values for $X$ and $x$?
2. How do you solve an equation if this expression equals a constant?
3. What if you had a coefficient in front of $X$ (e.g., $2X$)?
4. Can you graph this expression for specific values of $X$ and $x$?
5. How does this expression change if you substitute $x$ with $y$?

Tip: Always combine like terms to simplify an expression step by step, making it easier to solve or analyze.