I own Mission Impossible on the Apple IIc. Beat the game once as a kid. Each section (top to bottom like a tower) contains one code to open the elevator which vaporizes you. Each code you receive will fit in one of the 3 columns for the code. The symbols for the code are only available in the safes. Even if you have one for each column it doesn't mean it is the right code. You have to keep searching until you have the correct 3 symbols which allows you to enter the final elevator and brings you to the end of the game.
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