When a student used a calculator to calculate the average of 30 data, he mistakenly input one of the data 108 as 18, so what is the difference between the average and the actual average?

When a student used a calculator to calculate the average of 30 data, he mistakenly input one of the data 108 as 18, so what is the difference between the average and the actual average?

(108-18)÷30=3