Efficiency of Kareena and Krishna = 11.11 + 5.55 = 16.66%
Work done in 3 days = 3 x 16.66 = 50%
Rest work done by Kareena, Krishna and Shahid = 50/50 = 1 day
(Since efficiency of Shahid = 33%)
Thus in ( 3 + 1) days they have completed the work = 4 days.