The question asks you to analyze the expressions in Line 1 and Line 2 and to identify which property of addition is being applied.

Line 1:

$(7 + 1) + 9$ This is adding 7 and 1 first, then adding 9 to the result.

Line 2:

$7 + (1 + 9)$ This changes the grouping of the numbers, adding 1 and 9 first, then adding the result to 7.

This is an example of the associative property of addition, which allows us to change the grouping of the numbers being added without changing the sum.

Now, let's complete the steps in the question:

• In Line 1: $(7 + 1) + 9 = 8 + 9 = 17$
• In Line 2: $7 + (1 + 9) = 7 + 10 = 17$

Thus, the blanks can be filled in as follows:

• First blank: 8
• Second blank: 17
• Third blank: 10
• Fourth blank: 17

Completed Answer:

• $(7 + 1) + 9$ equals 8 + 9 which equals 17.
• $7 + (1 + 9)$ equals 7 + 10 which equals 17.

Do you want further details on the associative property? Here are five related questions:

1. Can you apply the associative property to subtraction?
2. How does the associative property work with multiplication?
3. Can you explain why the associative property is important in algebra?
4. How does the associative property differ from the commutative property?
5. Can you think of a real-world example where the associative property is useful?

Tip:

The associative property only applies to addition and multiplication, not to subtraction or division.