using formula to calculate a new date

using formula to calculate a new date

I have a date field that I want to use to calculate a new date field automatically using the data in the original date field.

I have tried using formulas but getting lots of syntax and missing quote errors.

This is what I've used....

Adddate (Newdate ${CustomModule1.Date of Valuation} + '90' 'DAYS')

Any help would be so gratefully received.

Kind regards