Method's Extension

Question

how to add a method's in a existing type
if an existing type is belongs to category Class but it is Sealed Class or it is belongs to Struct Category or We don,t have a Source Code of this type.

how ?
remember Sealed Class did not allow Inheritance
and Same in Struct and it is possible only if we have a Source code of existing type but this time
we Don't have.

Answer pls.

Answer 1

Real Gutch

Please add Java or the name of the language to the tags. So you can be helped faster.

Answer 2

Manual done

Answer 3

https://code.sololearn.com/cQ79d8DWT95V/?ref=app