Help plz? i don’t understand the example

The example is telling you to first add up each number then divide by the amount of numbers that are present in the set. There are four in this example.

Secondly the difference between each data point will differ from each number. Basically subtract the sum from each number. Which is 5 in this case. But if its negative flip it to a positive.

Then add up each absolute value and divide by 4 twice.