Alberto uses the steps below to solve the equation . 1/2x - 3 = 7 step 1: 1/2x - 3 + 3 = 7 + 3 step 2: 1/2x + 0 = 10 step 3: 1/2x = 10 step 4: 2(1/2)x = 2(10) step 5: 1x = 20 step 6: x = 20 which justifies step 6 of his work? 1.the addition property of equality 2.the identity property of addition 3.the multiplication property of equality 4.the identity property of multiplication