\(\frac{1}{v}=\frac{1}{30}-\frac{1}{40}\)

\(\frac{1}{v}=\frac{4-3}{120}\)

\(v=+120 \mathrm{\,cm}\)

Now, this image acts as object for the lens.

\(u=+120 \mathrm{\,cm}, f=30 \mathrm{\,cm}\)

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

\(\frac{1}{v}=\frac{1}{30}+\frac{1}{120}\)

\(\Rightarrow v=+24 \mathrm{\,cm}\)