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200 + owl height = tree height.
230 - tree height = owl height.
Since owl height is (230 - tree height), we have:
200 + (230 - tree height) = tree height.
Then add tree height to both sides:
200 + 230 - tree height + tree height = 2*(tree height).
Then
430 = 2*(tree height).
Then divide both sides by 2 to obtain
215 = tree height.
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