Object distance (u) = -25 cm (negative because the object is in front of the mirror)
Image distance (v) = +5 cm (positive because the image is behind the convex mirror)

Using  \(\frac{1}{f}\) = \(\frac{1}{u}\) + \(\frac{1}{v}\)

\(\frac{1}{f}\) = \(\frac{1}{-25}\) + \(\frac{1}{5}\)

f = \(\frac{25}{4}\) = 6.250cm.