The task asks to complete the expression and identify the missing property. Let’s solve it step by step:

1. The first equation is: $(3p + 1) + 2$

2. The second step shows: $= 3p + (1 + 2)$

This step uses the Associative Property of Addition, which states that you can regroup terms when adding without changing the result: $a + (b + c) = (a + b) + c$

3. In the final step, $1 + 2 = 3$, so: $= 3p + 3$

Final Answer:

• The missing property is: Associative property of addition.
• The completed blank is: $3$.

Do you want further clarification on this? Here are some related questions you might explore:

1. What is the difference between associative and commutative properties?
2. Can the distributive property apply to subtraction as well as addition?
3. Why is the associative property specific to addition and multiplication?
4. How do properties of addition simplify solving equations?
5. Can you provide a real-life example where the associative property is useful?

Tip:

When working with properties, focus on the operation (addition, multiplication) to determine which property applies. This avoids confusion between similar properties!