How to add days in date picker using form calculation widget?

I have a date entry field.  I want to take date entry, add 280 days, and return to subsequent date.

As you can see in the screenshot.  I convert the entry date to a number using Date(), add 280, then use DateValue() to convert that to a date.  Getting an unexpected date in 1970 as the result.

You can set the calculation like this (refer to my screenshot below).

Demo Form: https://form.jotform.com/91397940302963

For Example:
May 24, 2019 + 280 days then the result will be February 28, 2020. Is that the results you want to achieve?

Let us know if you are referring to something else.

That was it.  I made it more complicated than needed.