Write a function named postfixEval such that given a postfix expression, evaluate it and return the result.

Given a $($possibly empty$)$ string containing only alphabet letters and parentheses $(,),\{,\},[,],$ determine if the string is valid.

Given a $($possibly empty$)$ string, reverse it$.$

Example: Given input $$abcde$,$ your function should return $$edcba$$

$**$PLEASE USE THE STACK & CODE TEMPLATE PROVIDED IN PHOTO$**$