The height of the Blue Spruce would be 45 feet.
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.
1155 - 1110 = 45