Help with IF Function

Help with IF Function

Hello, 

I have different fields:

- CPQ TIME
- Reply (list field with 3 possible replies)
      - OK
      - SOON
      - LATE
- DATE ASKED
- DELIVERY TIME
- SIGNATURE DATE
- FINAL DATE

I need a function for final date. This field must be calculated based on the other fields.

If REPLY = OK, then final date is signature date + CPQ TIME

If REPLY = SOON, then final date must be SIGNATURE DATE + DELIVERY TIME

if REPLY = LATE, then final date must be DATE ASKED

I have tried to create the function for this formula field, but I can't find a way.

Thank you!