According to question , we can say that
P, Q, R, S, T, V and W are sitting in a straight line facing north. Each one of them lives on a different floor in the same building which is numbered from one to seven. Q sits fourth to the left of the person living on the 6th floor. W lives on the 3rd floor. The person living on the 1st floor sits third to right of S. S is not an immediate neighbor of W. Only one person lives between T and the person who lives on the 2nd floor.
Clearly , 2nd floor is required answer .
