AJO NowWithDelta using a field to set the number of days

This is a two part question. I am trying to use nowWithDelta to compare todays date to another date field and the difference between the two dates should be a second field (integer). My two questions are:

1. Is it possible to do arithmetic within nowWithDelta or is there another way to achieve this? nowWithDelta(10-7,"days"). 

2. Is it possible to use a field within nowWithDelta or is there another way to achieve this? nowWithDelta(#field, "days")

The end goal is to create an expression that does the following. I am open to other ways to set this up using something other than nowWithDelta:

GenericDateField > nowWithDelta(secondDatefield - 7, "days")