Can you solve this elementary school question from China?

This question is from the Hua Luogeng math competition in China. I was told it was for elementary school students (ages 10-12). There are many interesting ways to solve this question! Special thanks this month to: Daniel Lewis, Kyle, Lee Redden, Mike Robertson. Thanks to all supporters on Patreon!   / mindyourdecisions  

0:00 problem
1:05 method 1
5:36 method 2
7:22 method 3
9:48 method 4

Joshua Brown’s blog post (method 4)
https://thalestriangles.blogspot.com/...

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