Stacks - General Questions

Evaluate the postfix expression: 8 8 + 9 *

Evaluate the postfix expression: 9 3 - 3 +

Starting with an empty stack, these operations are performed: push(5), pop(), push(9), push(1), push(8), push(6), pop(). What is at the top of the stack now?

Evaluate the postfix expression: 4 2 * 7 4 * -

Starting with an empty stack, these operations are performed: push(2), push(2), push(7), pop(), push(1), pop(), pop(). What is at the top of the stack now?