Answer 1

Also I found this ,where you can experiment by changing symbols and understand it more clearly ,the result is in step by step too
https://www.web4college.com/converters/infix-to-postfix-prefix.php

Answer 2

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Answer 3

Symbol:5,+,9,*,(,8,+,3,)
Stack:none,+,+,+*,+*(,+*(,+*(+,+*(+,+*(+),+*
Expression:5,5,59,59,59,598,598,5983,5983+,5983+*+
Tried to understand it by here ,
https://www.google.com/search?ie=UTF-8&source=android-browser&q=infix+to+postfix+conversion+step+by+step#