Let us apply the formula and see what happens. Can we use the value of mean to find x now?

Think about how much the total of all the observations would increase.

Think about the total sum of observations for the mean 15 and mean 20.

Think about the methods which we can use to measure the central tendency.

take any number related to this

Find the total sum of all 15 observations. Then, find the total of first 8 and last 8 observations.