Let's tackle each expression step by step:

1. Simplifying $x^2 y + 4xy + 4$

This expression can be factored to simplify. Let's rewrite it:

$x^2 y + 4xy + 4$

Notice that $x^2 y + 4xy$ can be factored by factoring out $xy$:

$xy(x + 4) + 4$

The expression cannot be factored further without additional context or a common factor between $xy(x + 4)$ and $4$. Therefore, it seems we have reached the simplest form of the expression in its given state.

2. The Expression $y - 4$

This expression is already in its simplest form.

3. The Expression $x$

This expression is also already in its simplest form.

To summarize:

1. The expression $x^2 y + 4xy + 4$ cannot be simplified further without additional context.
2. The expression $y - 4$ is in its simplest form.
3. The expression $x$ is in its simplest form.

Would you like more details on these solutions or have any questions?

Here are some related questions you might find useful:

1. How do you factor polynomials with more than two terms?
2. What are some techniques for simplifying algebraic expressions?
3. Can you provide an example of factoring by grouping?
4. How do you determine if a polynomial can be factored further?
5. What are common mistakes to avoid when simplifying expressions?
6. How do you factor quadratic expressions in general?
7. Can you explain the process of polynomial division?
8. How does the distributive property help in factoring expressions?

Tip: Always look for common factors first when attempting to simplify or factor an expression. If no common factors exist, check for special factorizations or patterns, such as the difference of squares or perfect square trinomials.