To determine the missing step in proving the equivalence of the expressions \(12a + 10 + a\) and \(10 + a + 12a\) using the Commutative Property, we can look at the process of reordering the terms.
The missing step should involve rearranging the terms on the left-hand side expression \(12a + 10 + a\) to align with the structure of the right-hand side expression \(10 + a + 12a\).
By applying the Commutative Property, we can express this as:
Step 1: \(12a + a + 10 = 10 + a + 12a\)
This means we are just reorganizing the original left-hand side expression.
Therefore, the missing step in the proof is:
Step 1: \(12a + a + 10 = 10 + a + 12a\)
And after that, you proceed to Step 2, confirming that both sides simplify to \(10 + 13a\).