Answer:
15m
Step-by-step explanation:
change in real depth = 80 - 60 = 20m
Let us assume that the index is 4/3
Refractive index = change in real depth ÷ change in apparent depth
change in apparent depth = change in real depth÷ refractive index
= 20÷(4/3) = 20×(3/4) = 5×3 = 15m