Here are the simplified expressions with like terms collected:

1. $3a + 6b + 2a = 5a + 6b$
2. $9y + 8p + 9y - 3p = 18y + 5p$
3. $8k + 3u + 5u - 5k = 3k + 8u$
4. $7s + 4q + 5s + 3q = 12s + 7q$
5. $x - y + 4x + 4y = 5x + 3y$
6. $5d + 5d + s - 7d = 3d + s$
7. $2a + 3b + 5a - 3c - 4b + 5c = 7a - b + 2c$
8. $x + 2y + 3x - z - 4z = 4x + 2y - 5z$

Let me know if you need more details or further clarification!

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Relative questions:

1. How do you identify like terms in an expression?
2. What happens when you combine terms with opposite signs?
3. Why can’t terms with different variables be combined?
4. How can simplifying an expression help in solving equations?
5. What are the next steps after simplifying an algebraic expression?

Tip: Always ensure that like terms share the same variable and exponent when combining!