Questions

Parenthesis is not required because the order of the operators in the postfix /prefix expressions determines the actual order of operations in evaluating the expression

Hence, the missing number iss 25.

When you work at a call center you will come across irritated, angry, and abusive customers, you can say you will do that following to handle them:

-  Listen to them and empathize with their situation

-  Apologize and take ownership of the problem and give a solution

-  Approach them and ask for a reason for their displeasure

-  If they insist on talking to your manager, get him on line ASAP

- Follow up after giving the solution and ask for feedback