R must be recruited 6th, answer (B) is correct.
The reason is because of the Q-R rule. In question 6 we are told that Q must come immediately after W. If that is the case, then we also know that V must come before W. Therefore we have VWQ as a block chunk. If we try to put VWQ after P, we run out of space to put R, since R must come some time after Q. Thus, VWQ fills spots 1-3, P is in spot 4, and since S cannot be next to T, we must have one spot between them, which is where R will go, spot 6. So whether you put S into spot 5 and T into spot 7, or the other way around, R will still need to be in spot 6 in between S and T.