If the pianist who performs the first solo also performs the second solo, then which one of the following must be true?

I'm missing something important. While diagramming for this question I set up a scenario where W was in 1 & 2 and Z was in 5 and another scenario where Z was in 1 & 2 and W was in 5. I was in a stalemate over what must be true. I can't find the deduction for where Z can and can't go or rather, where W must go? I appreciate any guidance!