find it

u combide them in the item menu

I think you're thinking of Resident Evil zero 'cuz in the Resident Evil game, there is no briefcases puzzle to solve. Anyway, if it's for Resident Evil Zero, I know. There's one one after you use the long object to open up the airvent and Rebecca climb through it, dogs will jump out, take them out and then go to the end part near the door, there's a golden ring there. After that, go get the Hookshot gun to climb the window in the train section with the staircase, use the gun on the window and climb through, after that you should be on top of the train. Then jump down on the hole you see and there's a zombie here, kill it and you should find a jewelry box around the room. If you already have the brief case, examine the jewelry box and take the ring out, combine it with the briefcase, now combine the golden ring you found earlier with it and you'll find a card key. Otherwise, go take the briefcase and combine them, now you are able to open the door in the end of the train where the dead employee that you took the key from is.
PS: I still think you're talking about Resident Evil Zero.

ohhhhh i think your talking about resident evil zero