In order to get the mean/average of numbers, first, we need to know their sum. Then, divide it to the quantity of the numbers.
2 + 3 + 4 + 6 + 6 + 9 + 8 + 12 + 10 + 15 + 12 + 18 + 14 + 21 = 140
Quantity of the numbers = 14
140 ÷ 14 = 10
Therefore, their average/mean is 10.