d
\(1^{\text {st }}\) refraction in \(L _1\left( I _1\right)\)

\(\frac{1}{ v }-\frac{1}{ u }=\frac{1}{ f }\)

\(\frac{1}{ v }-\frac{1}{\infty}=\frac{1}{ f }\)

\(\therefore v = f\)

\(2^{2 dr } \text { refraction in } L _2\)

\(I _1 \rightarrow \text { object }\)

\(I _2 \rightarrow \text { image }\)

\(u =-40\,cm \quad f =20\,cm\)

\(\frac{1}{ v }-\frac{1}{ u }=\frac{1}{ f }\)

\(\frac{1}{ v }-\frac{1}{(-40)}=\frac{1}{20}\)

\(\frac{1}{ v }=\frac{1}{20}-\frac{1}{40}=\frac{6-3}{120}\)

\(\frac{1}{ v }=\frac{3}{120}=\frac{1}{40}\)

\(\therefore \quad v =40\,cm\)

Correct Answer is \(100.\)