I have created a infopath form like below
START DATE :
Happens Every: textbox drop down Weeks (Mon,thue,---sun)
Due Date :
Now when the user selects Start date as 7/2/2013, In the text box if he gives 3 and from drop down he selects Thuesday.
Now in Due Date it should display Next week Thursday date i.e (7/9/2013).
Similarly for ...