Problem with returning value from asynchronous function using callback

Here in my code, I want the processInput() to return the final result, but I am actually dealing with asynchronous function that returns a promise, so I am feeling harder to do it. Anyone can help me plz. My requirement is the function "processInput()" should return the result. https://code.sololearn.com/WAZ9kYhNzsaH/?ref=app