Find the distance of the image from object $O,$ formed by the combination of lenses in the figure:

$\left(1\right)$ Lens formula

$\frac{1}{v}-\frac{1}{u}=\frac{1}{f},$

$\frac{1}{v}-\frac{1}{-30}=\frac{1}{10}$

$\frac{1}{v}=\frac{1}{10}-\frac{1}{30}; \frac{1}{v}=\frac{3-1}{30};v=15 \mathrm{cm}$

$\left(2\right)$ $u=+10$

$\frac{1}{v}-\frac{1}{10}=\frac{1}{-10}$

$\frac{1}{v}=\frac{-1}{10}+\frac{1}{10} v=\infty$

$\left(3\right)$ Ray will converge at focus of 30 cm right of third lens.
it.$v=+30 \mathrm{cm}$ (from third lens)