Solution:

For a convex mirror, \(f = +10\text{ cm}\) and magnification is virtual and erect, so \(m = +\frac{1}{3}\). Using \(m = \frac{f}{f-u}\), we get \(\frac{1}{3} = \frac{10}{10-u} \implies 10-u = 30 \implies u = -20\text{ cm}\). The distance is \(20\text{ cm}\).