Correct Answer - C
`(1)/(f_(film))=(n_(1)-1)((1)/(R)-(1)/(R)) rArr f_(film)=infty` (inf inite)
`therefor` No effect of presence of film.
For Air to glass
Using single spherical Refraction :-
`(n_(2))/(v)-(1)/(u)=(n_(2)-1)/(R)`
`(1.5)/(v)-(1)/(infty)=(1.5-1)/(R) rArr v=3R`
`therefore f_(1)=3R`
For Glass to Air `( :-)/`
`(1)/(v)-(n_(2))(u)=(1-n_(2))/(-R)`
`rArr (1)/(v)-(1.5)/(infty)=(1-1.5)/(-R)`
`rArr v=2R`
`therefore f_(2)=2R`