Supposed blue spruce was included in the list and the mean decreased to 165 what is the height of the blue spruce?

The height of the blue spruce was 45.

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:

(160+320+100+110+200+220+x)/7 = 165
(1110+x)/7 = 165

Multiply both sides by 7:
1110 + x = 1155

Subtract 1110 from both sides:
x = 45

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