Complete #2 in Java

1) Evaluate the following post-fix expressions or state why the expression is invalid: a. 52* 35143+-98-** k a b. 694 /+7 2) Using only emptyCheck, top, push, and pop operations, write a function that returns the middle value from a stack S, where the middle of a stack of size n is the INT((n+1)/2)th element. You may create additional stacks as needed