Stacks - General Questions

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

Evaluate the postfix expression: 9 3 9 * +

Starting with an empty stack, these operations are performed: push(6), pop(), push(4), pop(), push(1), pop(), push(8). What is at the top of the stack now?

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

Convert the infix expression (A+B)*(C-D)/E to postfix.