Four person P, Q, R, S were engaged for doing a task, with the condition that P; Q; R; S work respectively,on (Mondays, Thursdays); (Tuesdays, Fridays); (Wednesdays, Saturdays); (Sundays). The task was began on a Monday,and got completed on the $$15^{th}$$ day, which was also a Monday.If the efficiencies of P, Q, R, S in respect of doing this task were in the proportion 1 : 2 : 3 : 4,then in how many days could R completed the task,working alone without break?