Answer:
C. 9.9 cm
Step-by-step explanation:
The location of the object, u = 14 cm
The location of the image, v = 5.8 cm
The focal length of the mirror, f = Required
The mirror formula for a convex mirror is given as follows;

Therefore, we get;

Therefore;

The focal length of the mirror, f ≈ 9.9 cm