Answer:
Tree is 45 ft tall.
Explanation:
In the figure attached AB is the tree and CD is the yardstick.
Shadow of tree AB is BO = 15 ft and shadow of yardstick is CO.
since length of a yardstick is = 1 yard or 3 ft.
Now we know that ΔABO and ΔDCO are similar.(since ∠A = ∠D and ∠B = ∠C = 90° so AA property proving triangles similar)
Therefore

By putting the values of AB and CD

x = 3×15 = 45 ft.
Therefore the height of the tree is 45 ft.