Stacks - General Questions

Starting with an empty stack, these operations are performed: push(9), push(8), pop(), push(4), pop(), push(4), push(1). What is at the top of the stack now?

Starting with an empty stack, these operations are performed: push(9), pop(), push(6), push(2), pop(), pop(), push(7). What is at the top of the stack now?

Which application uses a stack?

Starting with an empty stack, these operations are performed: push(6), push(8), push(7), push(1), push(5), pop(), pop(). What is at the top of the stack now?

Starting with an empty stack, these operations are performed: push(5), pop(), push(7), pop(), push(7), push(6), pop(). What is at the top of the stack now?