How to add a number (ie. 8) to a date to output a date +8 days from starting date?

Is there a way that I can type in a date let's say 12-8-17 in a cell, then in another cell have a variable number ie. 8, then combine them together in another cell that would give me 12-16-17? Do I have to convert 12-8-17 to an epoch number, then convert 8 to an epoch number as well, add them both together and then convert back into a date? If so I'm not sure how to do that in numbers. Let me know thanks!