Answer: 15 feet
Explanation:
Hi, since the situation forms a right triangle (see attachment) we have to apply the next trigonometric function.
Tan α = opposite side / adjacent side
Where α is the angle of elevation to the sun, , the opposite side (x) is the height of the tree, and the adjacent side is the length of the shadow.
Replacing with the values given:
Tan 31 = x /25
Tan 31 (25) =x
x = 15 feet
Feel free to ask for more if needed or if you did not understand something.