please help me with this C++ problem. dont forget the explanation. thank you!!!!

5. Write a C++ program to evaluate the value of an arithmetic expression in Reverse Polish Notation (known as postfix expression). Valid operators are +,-, *,/. Each operand may be an integer or another expression. Example: Input: {"2", "l", "+", "3, *"), Output: 9; Explanation: ((2+1))*3-9 Input: {4, 13, 5, ", "+"), Output: 6: Explanation: (4+(13/5))-6