To simplify the expression $2x + 6y + 7x + 4 - 6y$, let's combine like terms.

1. Combine the $x$-terms: $2x + 7x = 9x$

2. Combine the $y$-terms: $6y - 6y = 0$

3. Lastly, the constant term remains as it is: $+ 4$

Putting it all together: $9x + 4$

So, the simplified expression is: $9x + 4$

Would you like more details, or do you have any questions?

Here are some related questions for further exploration:

1. How do you simplify expressions with more variables, like $2x + 6y + 7z + 4 - 6y$?
2. How do you handle expressions with exponents when simplifying?
3. What are some common mistakes to watch for when simplifying expressions?
4. How can you verify that an expression is fully simplified?
5. How does simplification change when there are parentheses involved in the expression?

Tip: Always start by grouping like terms, such as terms with the same variable or constants, to simplify expressions efficiently.