Fei

X Cannot work Sundays, Saturdays

George

X Cannot work even numbered Fridays

Helen

$$ Cannot work odd numbered Wednesdays

Ian

Must always work Mondays

Question

Three people must be on duty at all times. On what dates could lan start a $3$ day ve$$ation$?$

Calendar

$\backslash$table$[[$SUN$,$MON,TUE,WED,THU,FRI,SAT$],[,,,1,2,3,],[4,5,6,7,8,9,10],[11,12,13,14,15,16,17],[18,19,20,21,22,23,24],[25,26,27,28,29,30,]]$