Fill in the blanks so that the equality holds. Also state the property used in each case.
`234+(555+787)=(234+"___________")+787`

Options

A. `787`, Addition is commutative for whole numbers
B. `555`, Addition is associative for whole numbers
C. `555`, Addition is commutative for whole numbers
D. `787`, Addition is associative for whole numbers

Answer

To solve the equation \( 234 + (555 + 787) = (234 + "___________") + 787 \), we need to fill in the blank so that the equality holds.

### Step-by-Step Solution:

1. **Understand the Expression**: The left side of the equation is \( 234 + (555 + 787) \). We need to simplify the expression inside the parentheses first.

2. **Calculate the Sum Inside the Parentheses**:
\[ 555 + 787 = 1342 \]
So, the left side becomes:
\[ 234 + 1342 \]

3. **Calculate the Total**:
\[ 234 + 1342 = 1576 \]

4. **Set Up the Right Side**: Now we need to fill in the blank on the right side of the equation:
\[ 234 + ( \text{blank} ) + 787 = 1576 \]

5. **Rearranging the Right Side**: We can rearrange the right side to isolate the blank:
\[ (234 + \text{blank}) + 787 = 1576 \]

6. **Subtract 787 from Both Sides**:
\[ 234 + \text{blank} = 1576 - 787 \]
Calculate \( 1576 - 787 \):
\[ 1576 - 787 = 789 \]

7. **Isolate the Blank**:
\[ \text{blank} = 789 - 234 \]
Calculate \( 789 - 234 \):
\[ 789 - 234 = 555 \]

8. **Fill in the Blank**: Therefore, the blank should be filled with \( 555 \).

### Final Answer:
The completed equation is:
\[ 234 + (555 + 787) = (234 + 555) + 787 \]
The property used here is the **Associative Property of Addition**.