We find the mean by adding all of the data points and dividing by the number of data points. We will add the unknown value x and change the number we're dividing by to 7:
If you add all of the value right now, you will have 1110.
With the addition of the Blue Spruce, we will have 7 trees. If we multiply the new mean of 165 by 7, we get 1155. This is the amount we need to have the correct mean.
Subtract to find the difference needed by the Blue Spruce.
