Why Can't M be Used in Q for Scenario 1

Hello, In the video explanation, the speaker says "we know M can't be in Quality" for scenario #1 but how do we know that M can't be in Q and used twice rather than having K in Quality and used exactly twice? ex: #1 P: FGH Q: FLM S: GKM #2: P: FGH Q: GMK S: FKL Why doesn't this work?