The last number would be 10.
In order to find this, we need to know the total of all of the numbers. To do that, multiply the amount of numbers by the average.
4 * 8 = 32.
So we know all the numbers add up to 32. We also know the first 3 add up to 22. So if we subtract the first 3 from the overall total, we can get the fourth number.
32 - 22 = 10
