45 m
80 m
15 m
60 m
Correct answer is C
Refraction index (n)= (Real depth)/App. depth
For 80 m Real depth: (4)/3 = (80)/App. depth
App. dept = (80 x 3)/4 = 60 m
For 60 m real depth; (4)/3 = (60)/ App. depth
App. depth = (60 x 3)/4 = 45 m
∴change in App. depth = 60 -45 = 15 m