I am completing a 1040A for my mother. As I try to determine the taxable part of the pension my father left for her I get a negative number on the simplified method worksheet (line 7). I am stumped - do I enter a 0 instead. I have been filling out this form for about 5 years now and this is the first time I've run into this. I know the cost in the plan and used previous year's values for line 4. I am not sure what this is really trying to tell me.

Any guidance would be greatly appreicated.