1st field = recd date
2nd field = due date
3rd field = elapsed
in the elapsed field set field type = calculation then add due date - recd date.
Subtracting the date fields gives you the difference in days. To get the number of weeks you'd then divide by 7 of course.
But when we divide by 7 if we get 1.5, how to represent that in weeks? can we do the calculation in table itself?
You can format the field to any number of signifiant digits that you like. Or, you can do it in the calculation, using the "Round" number function.