How can I approach this question to solve?

A liquid of refractive index mu1 = 2 is filled in a thin glass sphere of radius 20 cm. A fish is moving towards the centre of sphere with a speed of 2cm/s.Find speed of image of fish in mirror, when fish is at distance 10 cm from the centre of sphere as shown in the figure.(Sorry can't attach image as subreddit doesn't allow) Information from image-Sphere filled with mu1=2 liquid and plane mirror on the right side of sphere travelling at speed 4cm/s towards right direction.