To determine the missing step in proving the equivalence of \( 12a + 10 + a = 10 + a + 12a \) using the Commutative Property, we need to rearrange the terms on the left side so that they match the right side.
The left side \( 12a + 10 + a \) can be rearranged to \( 10 + a + 12a \) by first applying the Commutative Property.
Thus, the missing step should be:
Step 1: \( 12a + a + 10 = 10 + a + 12a \)
In this case, you can group the \( 12a \) and \( a \) together. So, the correct missing response is:
10 + 12a + a = 10 + a + 12a.
However, since this option doesn't exist directly, the correct logical choice is:
12a + 10 + a = 10 + 12a + a
which is a valid application of the Associative and Commutative properties combined, but it doesn't seem explicitly listed.
Among the given options, the correct missing step most closely represented is:
10 + 12a + a = 10 + 13a.
This option correctly illustrates that you can rearrange and combine like terms to simplify the expression to achieve step 2.
So, my conclusion regarding the missing step would be:
10 + 12a + a = 10 + 13a.