To find the mean of a set of numbers, you need to add up all the numbers and then divide by the number of numbers in the set.
In this case, the mean of the four numbers is 12, which means the sum of those four numbers is 4 × 12 = 48. The mean of the other six numbers is 22, which means the sum of those six numbers is 6 × 22 = 132. The sum of all ten numbers is therefore 48 + 132 = 180.
To find the mean of all ten numbers, we need to divide the sum by the number of numbers, which is
= 18. Therefore, the mean of all ten numbers is 18.