An object is placed at a distance $d = 30$ cm from a converging lens of focal length $f = 10$ cm. Find the distance $d'$ from the lens to the image of the object.
The thin lens formula:
$$\frac{1}{f} = \frac{1}{d} + \frac{1}{d\prime}$$
$$\frac{1}{d\prime} = \frac{1}{f} - \frac{1}{d} = \frac{1}{10} - \frac{1}{30} = \frac{3 - 1}{30} = \frac{2}{30} = \frac{1}{15}$$
$$d\prime = 15 \text{ cm}$$
$d' = 15$ cm