Answer: 28.71 km
Step-by-step explanation:
For the convex mirror (ocean):
Radius of curvature = 6.4*10^3 km
Focal length (f) = R/2 = 3.2*10^3 km
Object distance (u) = -3.84*10^5
Mirror formula:



v = 3173.55km
Magnification,
So, height of image/height of object = 3173.55/3.84*10^5
Diameter of image = 3173.55/3.84*10^5 * 3475
Diameter of image = 28.71 km
Therefore, the diameter of the image is 28.71 km