IF Statement: Dates in multiple columns

[Swebb]

Hi,
I do not use If statements very often... so I am hoping someone can give me a hand!
I have three columns of data containing dates. The formula I am trying to build will need to look at the first coulmn. If it is populated, the output should be that date. If it is blank, then I would like to use the date in the second column + 7 days... and if that is blank I would like to use the date in the last cloumn + 28 day. If they are all blank the result should be "blank". Can anyone help me out? Thanks