If Then rule with dates help

Hello,

I'm trying to figure out a formula to calculate adding 84 days to an original date. However, if the calculated date does not fall on a Sunday, to add those days until it does. So for example, if you add 84 days to today's date, it is 12/11/2015, but it falls on a Friday. How can I add the If rule to have it add the 2 days to make it Sunday?

Thanks!