State tax filing

If you look on Line 20 on the actual form, that number is always positive, but there is a box to the left of it where you would enter a "-" sign to indicate that the number is negative. If line 20 was negative, then line 23 should be added to it to arrive at line 24, since they are both subtractions.

It may be that you have the standard deduction of $2,200 (single) or $4,400 (joint filer) in box 23, so the charitable contributions are not tax deductible.