\(\frac{1}{v} - \frac{1}{u} = \frac{1}{f}\) ; \(\frac{1}{v} + \frac{1}{{20}} = \frac{1}{5}\)
\({v=\frac{20}{3}\, \mathrm{cm}}\)
Image by concave lens:
\(u=\left[\frac{20}{3}-2\right]=\frac{14}{3} \,\mathrm{cm}\)
\(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\) ; \(\frac{1}{v}-\frac{3}{14}=-\frac{1}{5}\)
\(v=70\, \mathrm{cm}\)