in the below question @=lamda

when one of the slits in the young's experiment is covered with a transparent sheet of thickness 3.6*10^-3 cm the central fringe shifts to a position originally occupiod by the 30th fringe.If  @=600 amstrom , the refractive index of the sheet is

 

(A) 1.50                                                     (B) 1.7

 

(C) 1.60                                                     (D) 1.8

 

choose the correct option