You can set up an inequality to solve this. You can either do big to small -->
or small to big -->
. I'm going to be using big to small because I think it's a little easier.
![(20)/(8) = (x)/(18)](https://img.qammunity.org/2019/formulas/mathematics/high-school/jirwdkzp6hook981c9o79t0v0kj39u9is3.png)
Cross multiply and you will get:
![360 = 8x](https://img.qammunity.org/2019/formulas/mathematics/high-school/4fzsskdfbmkwkb6c6gdygbpfplioy6eqga.png)
Isolate x:
![x = (360)/(8)](https://img.qammunity.org/2019/formulas/mathematics/high-school/n2isbcdmfd0tmhbpb9binm6jd7ksefhz9a.png)
x =
![(90)/(2)](https://img.qammunity.org/2019/formulas/mathematics/high-school/anter3qizybe6nat1h9vvfk8o0e8x4ufza.png)
x = 45
The goal post is 45 feet tall. Hope this helped. Good luck. : )