Let focal length of convex lens of glass `=f_(1)=30cm` focal length of plano concave lens of liquid `=f_(2)` combined focal length. F = 45.0 cm
As `(1)/(f_(1))+(1)/(f_(2))=(1)/(F)`
`(1)/(f_(2))=(1)/(F)-(1)/(f_(1))=(1)/(45)-(1)/(30)=(-1)/(90)`
`f_(2)=-90 cm`
For glass lens, let `R_(1)=R, R_(2)=-R`
As `(1)/(f_(1))=(mu-1)((1)/(R_(1))-(1)/(R_(2)))`
`(1)/(30)=((3)/(2)-1)((1)/(R)+(1)/(R))`
`=1//2xx2//R=1//R`
R = 30 cm
For liquid lens
`R_(1)=-R=-30.0cm, R_(2)=oo`
`(1)/(f_(2))=(mu-1)((1)/(R_(1))-(1)/(R_(2)))`
`=(mu-1)((1)/(-30)-(1)/(oo)) or (1)/(-90)`
`=-(mu-1)xx(1)/(-30)`
`mu_(1)-1=(30)/(90)=(1)/(3), mu_(1)=1+(1)/(3)=(4)/(3)`