Correct Answer - `- 5 cm, -15 cm`
Here, `f = 10 cm`, object distance, `u = ?`
In a convex lens, as the image can be real as well as virtual, magnification, `m = v/u = +-2`
or `v = +-2u`
As `(1)/(f) = (1)/(v) - 1/u, 1/10 = 1/(+-2u) - 1/u = (+-1-2)/(2u)`
Thus, either `1/10 = - 1/(2u) or 1/10 = - 3/(2u)`
Clearly, `u = - 5 cm, u = -15 cm`