To determine the missing step in the proof of equivalence between \( 12a + 10 + a \) and \( 10 + a + 12a \) using the Commutative Property, we need to show how we can rearrange the terms.
The expression \( 12a + 10 + a \) can be rearranged as follows:
1. **Step 1: 10 + 12a + a = 10 + a + 12a**
This rearrangement is valid by the Commutative Property, which states that the order of the terms can be changed in addition.
Now we can conclude:
- **Step 2:** The equation can also be written as \( 10 + 13a = 10 + 13a \) through combining like terms \( 12a + a = 13a \).
- **Step 3:** Finally, since both expressions evaluate to the same form, we can state they are equivalent.
Therefore, the correct response for the missing step is:
**10 + 12a + a = 10 + a + 12a**