Answer:
![\displaystyle CD=BE\ (CA)/(BA)](https://img.qammunity.org/2021/formulas/physics/high-school/psn5n33ul8hlx0il5fze9j13syxusnmqth.png)
Step-by-step explanation:
Thales Theorem
It applies when a line is drawn parallel to one side of a triangle and it intersects the other two sides. The theorem states that line divides the two sides in the same ratio or proportion.
We have drawn the triangle that describes the situation stated in the question, where we want to know the value of CD, knowing the values of BE, BA, and CA. The red line BE is parallel to the line CD, so the Tales theorem must stand meaning that the sides AC and AB are proportionally divided at the same ratio as CD and BA, thus
![\displaystyle (CD)/(BE)=(CA)/(BA)](https://img.qammunity.org/2021/formulas/physics/high-school/wctc1gwyh2e5qcvc0ln90ikc8fmwfqmsv4.png)
We can solve for CD (the height of the flagpole)
![\boxed{\displaystyle CD=BE\ (CA)/(BA)}](https://img.qammunity.org/2021/formulas/physics/high-school/hzmpczv7pyaaop40cz0kc8hh9qekrs05iz.png)