can't create a total field between three tables

Hi,
I am using MS Access 2010 on Windows System 7.

I have three tables: A, B, C
Table A has the field Task NO
Table B has the fields Task No, PriorActuals
Table C has the fields Task No, HoldbackActuals

I need to create a query that tasks the Task No from Table A and matches it to Table B and Table C. I then need to show in the query the following:

Task no PriorActuals HoldbackActuals Total

My problem is that depending on how I connect the tables, different values are stored in the Total field. the Total field will either be all the data in the PriorActuals field or it will be all the data in the HoldbackActuals field. I can't get the total field to show PriorActuals + holdbackActuals.

Please help. i have tried everything I can think of and I can't get it to work.

Thanks