A new bank has decided to stay open only on weekends - all day Saturday and Sunday - and no other days. The bank has hired two managers (U and V), Four tellers (W,X,Y, and Z), and two operation officers (S and T), for a total of exactly eight full-time employees.

No part-time employees are hired.
Each employee works a complete day when working.
A manager must be on duty each day.
The managers cannot work on the same day.
At least two tellers must be working on the same day.
W and X will not work on the same day.
S and Z will only work on Saturday.
No employee can work on consecutive days, but each employee must work on Saturday or Sunday.

If W works on Sunday, then which one of the following must be true?