Suppose an initially empty stack, S, has performed a total of 75 push() operations, 5 peek() operations and 10 pop operations, 4 of which returned null to indicate an empty stack. What is the current...

Suppose an initially empty stack, S, has performed a total of 75 push() operations, 5 peek() operations and 10 pop operations, 4 of which returned null to indicate an empty stack. What is the current size of the stack, S? (Explain your answer/Show your workings)