Add Days to a Date field

Hi all,

I have the following requirement:

I have a date field 0calday and the user would like to add a specific no.of days to it, like for example 10 or 15 days. Then we use this computed date field in calculations in the query. Could you please help and let me know how we can no.of days to a date field? And also how we can compute no.of days between two date fields?

Regards,

Ashmith Roy