To determine the missing step in your proof, we need to apply the Commutative Property to rearrange the terms.
The expression we start with is \(12a + 10 + a\). We can rearrange the terms using the Commutative Property of Addition, which states that changing the order of addends does not change the sum.
Therefore, the missing step should be:
Step 1: \(12a + a + 10 = 10 + 12a + a\)
After this step, you can combine \(12a + a\) to get \(13a\), leading to:
Step 2: \(10 + 13a = 10 + 13a\)
Finally, you conclude that the expressions are equivalent because they both equal the same value.
So, the answer would be:
12a + a + 10 = 10 + 12a + a.