Exhaust Downpipe bolt is stuck

(99 V6) So I have an issue with my downpipe ATM. My driver-side downpipe has a bolt that seems stuck, and I'm not quite sure what size of a bolt I need to get for my year. One of the bolts is fine, but because one of them isn't there, I currently have an exhaust leak. Kinda makes it sound ty when Im driving, even with my aftermarket pipes.

Does anyone know the size/thread of the bolt+nut that I need to get so I can finally fix this thing? And if you know any places such as Autozone or AAP have them? And any idea on how to get this stuck bolt removed?

Edited it, it's actually stuck, not missing. I'm not quite sure on how to get this thing out.