How many stringers?

[Mulv80]

I know for sure that the bulkhead in front of the gas tank is rotted. The girders feel like they have separated from the wood in some spots. I was going to remove the tank, replace the bulkhead then inspect the girders. I really don't want to cut the floor. The floor is solid and doesnt have any cracking. I nearly have the tank out, hopefully this weekend I can get in there.