need help freeze plug problems

I have a inline 200 and I not sure if its called a freeze plugs but something fell out and its a plug that says its 25mm and i was wondering where its goes and how many are there of them. I think I saw four right under the header and all four are pluged. Please help.

it fell out[img]/phpBB/images/smiles/icon_frown.gif[/img]or did ICEpush it out
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i started it and i thought it was going and let the key go and then the engine stalled then it made a pop sound and it flew out i cant find where it goes

not sure if this helps but it is a 78 block and a 73 head