Which property was used to simplify the expression? 3c+9 +4c=3c+4c+9

Three consecutive even numbers have a sum between 84 and 96. a. write an inequality to find the three numbers. let n represent the smallest even number. b. solve the inequality. a. 84 ≤ n + (n + 2) + (n + 4) ≤ 96 b. 78 ≤ n ≤ 90 a. 84 < n + (n + 2) + (n + 4) < 96 b. 26 < n < 30 a. 84 < n + (n + 1) + (n + 2) < 96 b. 27 < n < 31 a. n + (n + 2) + (n + 4) < –84 or n + (n + 2) + (n + 4) > 96 b. n < –30 or n > 31