*SOLVED* Can't get JavaScript to recognize variations

Question

Started learning JavaScript two days ago.
I've been trying to make simple mathematical function but JavaScript won't recognize variations given from prompts.

https://code.sololearn.com/WTO4Rs03yViU/?ref=app

Answer 1

Instead of local variables, declare the a and b variable as global

Answer 2

addNum function doesn't know about variable a or b. either do what Calvin said or return a and b from top function get store it on addNum function