Here, focal length of lens, `f = -15 cm`,
image distance, `v = -10 cm`, object distance, `u = ?`
From `(1)/(f) = (1)/(v) - 1/u`
`1/u = (1)/(v) - (1)/(f) = 1/(-10) + 1/15 = (-3 +2)/(30) = (-1)/30`
or `u = - 30 cm`.
The ray diagram of image formation is shown in Fig.