We are asked to find which expression is equivalent to the expression:

$2x + 3y - x - (8 + 1)$

Let's simplify this step by step.

Step 1: Simplify the parentheses

First, simplify $8 + 1$: $8 + 1 = 9$ So the expression becomes: $2x + 3y - x - 9$

Step 2: Combine like terms

Now, combine the terms involving $x$: $2x - x = x$ So the expression simplifies to: $x + 3y - 9$

Final simplified expression:

$x + 3y - 9$

Now, let's look at the answer choices. The correct one is:

$\boxed{x + 3y - 9}$

Do you want further details on any of these steps?

Here are 5 related questions you might explore:

1. How can you combine like terms in more complex algebraic expressions?
2. What happens if the expression inside the parentheses has a negative sign outside?
3. How can you factor expressions like the one above?
4. How do you solve for $x$ or $y$ if given a specific value for the other variable?
5. How can we rearrange this expression to represent it in a different format?

Tip: Always simplify terms inside parentheses first before performing other operations in the expression.