Answer: 1.86 ft.
Explanation:
Let x be the height of tree.
Given: A tree casts a 6.5 ft shadow at the same time that a person 9 ft tall casts a 31.5 ft shadow.
Since both the tree and the man are standing vertical to the ground at the same time so the sun rays will make the same angle , therefore, the triangles made by both tree and man are similar.
And in the similar triangles, the sides are proportional.
Therefore,

⇒

⇒

Hence, the height of the tree is 1.86 ft.