Billing for two Free-tier EC2 instances

Hi, I understand that for EC2 instances, you get 12 months of 750 hours per month for free-tier EC2 instances. I'm wondering that if I have two running EC2 instances, how will I be billed? I looked at the billing calculator and tried calculating for an EC2 t2.micro instance but there are many billing options that appeared that were a little confusing. If I have two EC2 instances running, which would be about ~1400 hours per month, how would I be billed? Is it the On-demand payment option? How do I know which payment option I am on?