Stacks - General Questions

Starting with an empty stack, these operations are performed: push(7), pop(), push(4), push(4), push(7), push(1), push(7). What is at the top of the stack now?

Evaluate the postfix expression: 5 2 4 * +

Starting with an empty stack, these operations are performed: push(1), push(1), push(5), push(7), pop(), push(7), push(9). What is at the top of the stack now?

Evaluate the postfix expression: 9 9 + 8 *

Evaluate the postfix expression: 8 2 - 4 +