What Chain Does This Use?

Everything's rusted, all I want to do is get this bike workin but I don't know the language to look it up. I try looking up like "how to find out what type of chain my bike needs", and then I get "count the speed"? This bike looks simple enough, no zigzag chain things or anything, just a normal bike. Any suggestions? I'd buy a new one if they weren't so expensive, and getting it tuned at a place costs the same as just getting a new one