First, we are going to draw a picture for the problem
We can formulate the following equation, given that we can use triangle similarity theorem.
![\frac{\text{Andy height}}{x\text{ (post height)}}=\frac{\text{shadow of Andy}}{\text{Shadow of the post}}](https://img.qammunity.org/2023/formulas/mathematics/college/frhzchz2tn8yzko4whpha07xo7itm3qok2.png)
Replacing the values we have
![\begin{gathered} (5)/(x)\text{ = }(9)/(35) \\ 5\cdot(35)/(9)=x \\ 19.4\text{ = x} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/6bfudqe86yny0m3tqa11p9u37fpmogyyrl.png)
Isolating x, we get x is equal to 19.4 ft, which is the height of the post.