Answer:
The yield of the stand if one-tenth of the trees are cut is 360000 board-feet.
Step-by-step explanation:
First, let is find the total amount of fir trees that occupies the area of 24 hectares. (1 hectare = 10000 square meters)

Where:
- Surface density, measured in trees per square meter.
- Total area, measured in square meters.
Given that
and
, the total amount of fir trees is:


It is known that one-tenth of the tress are cut, whose amount is:



If each tree will yield 300 board-feet, then the yield related to the trees that are cut is:

Where:
- Yield of the tress, measured in board-feet per tree.
- Amount of trees that will be cut, measured in trees.
If
and
, then:


The yield of the stand if one-tenth of the trees are cut is 360000 board-feet.