Answer :
Focal length of convex lens is taken positive.
[tex]:\implies\sf\:\dfrac{1}{v}-\dfrac{1}{u}=\dfrac{1}{f}[/tex]
[tex]:\implies\sf\:\dfrac{1}{v}-\dfrac{1}{(-30)}=\dfrac{1}{20}[/tex]
[tex]:\implies\sf\:\dfrac{1}{v}=\dfrac{1}{20}-\dfrac{1}{30}[/tex]
[tex]:\implies\sf\:\dfrac{1}{v}=\dfrac{3-2}{60}[/tex]
[tex]:\implies\:\boxed{\bf{\gray{v=60\:cm}}}[/tex]
