post entries but keep formulas

[cfinch100]

hi
i need to be able to keep formuas in t2:t50 (sheet3) when items are posted from sheet3 by sheet(frmissued),i enter a date in sheet3 h2:h50 which gives me a due date (7 days later ) in t2:t50, but when i save sheet and delete entries it also deletes the formula in t2:t50,how can i make t2:t50 reset to =h2:h50+7
any help would be good please
cheers colin