Fill in the blanks and state the property used.
`15+(-45)= "_______" +15`

Answer

To solve the question `15 + (-45) = "_______" + 15`, we need to fill in the blank and state the property used.

### Step-by-Step Solution:

1. **Understand the Expression**: We start with the expression `15 + (-45)`. This means we are adding 15 and -45.

2. **Calculate the Left Side**:
- When we add 15 and -45, we can think of it as subtracting 45 from 15.
- So, \( 15 + (-45) = 15 - 45 = -30 \).

3. **Fill in the Blank**:
- Now we need to rewrite the expression in the form of `_______ + 15`.
- We know that `15 + (-45)` equals `-30`.
- Therefore, we can write `-30 + 15` to fill in the blank.
- So, the blank is filled with `-30`.

4. **Final Expression**:
- Now we have `15 + (-45) = -30 + 15`.

5. **State the Property Used**:
- The property used here is the **Commutative Property of Addition**. This property states that the order in which two numbers are added does not change the sum.
- In mathematical terms, \( a + b = b + a \).

### Final Answer:
The filled blank is `-30`, and the property used is the **Commutative Property of Addition**.