Adding 5 variables when 2 variables are null , in this total value not showing?

Dear all
I have applied … (if(${CIG_Grade}=’’,0,${CIG_Grade}))+(if(${Grade_20}=’’,0,${Grade_20})) or coalesce(${CIG_Grade},0)+coalesce(${Grade_20},0) does not any of these.

I have two groups in the form 1. CIG_Grade 2. Grade_20
When I select 1. CIG_Grade then 2. Grade_20 not displayed.
input 1. CIG_Grade then result show 0

When I select 2. CIG_20 then 1. CIG_Grade not displayed.
input 2. CIG_20 then result show 0

I need any of one group result.