Question 1153480
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With the problem presented as it is, the person's distance from the tree is irrelevant.<br>
Assuming the tree and the person are standing perpendicular to the ground, the triangles formed by the tree and the person, their shadows, and the rays of light that produce the shadows are similar right triangles.<br>
According to corresponding parts of similar triangles,<br><pre>
tree's height     person's height
-------------  =  ---------------
tree's shadow     person's shadow</pre>
{{{x/86 = 5/6}}}<br>
{{{x = (5/6)*86 = 430/6 = 215/3}}} or 71 2/3 feet<br>