Question

Indicate which property is illustrated in Step 2.

Step 1 3x + 6 + 12x + 7 = (3x + 6) + (12x + 7)
Step 2 = 3x + (6 + 12x) + 7
Step 3 = 3x + (12x + 6) + 7
Step 4 = (3x + 12x) + (6 + 7)
Step 5 = (3 + 12)x + (6 + 7)
Step 6 = 15x + 13

commutative
distributive
associative
arithmetic fact