To determine the missing step using the commutative property, we need to rearrange the terms in the expression, which states that the order of addition does not affect the sum.
Step 1: 12a + 10 + a = 10 + 12a + a
The expression can also be rearranged as \(10 + a + 12a\) (keeping \(10\) and \(a\) first).
Thus, the complete proof would be:
Step 1: 12a + 10 + a = 10 + 12a + a
Step 2: 10 + 13a = 10 + 13a
Step 3: The expressions are equivalent because they both equal the same value.
To clarify the options you provided, the correct missing step is:
12a + 10 + a = 10 + 12a + a.