Answer:
Oak tree is 33 ft tall.
Explanation:
We know that Irene places a mirror on the ground and walks backwards such that the mirror is in between her and the oak tree (as shown in the attached picture).
Given the distance of Irene's eyes from ground, distance between oak tree and mirror and distance between mirror and Irene, we are to find the height of the tree.
For this, we will use the ratio method:

T = 33 ft