1095 A - Twor forms

I have 2 1095 A, 

the first one entered is fine. 

The second form I enter A is @272.35  and B and C is blank. 

At first enter zero and deleted form as I saw the question in this chat. 

I started a new form it says line B and  C cannot be less then zero. 

The answer posted was to leave it blank. I did leave it bland I still have the error.