The sum of the two vectors in A, B, and C is equal to the sum of the two vectors above the line. The sum of the two vectors in D isn't.
You have learned your lesson well, Suhay. Your statement is correct.
The light rays from the fish BEND when they flow out of the water into the air. But our primitive brain still believes that the light rays flow STRAIGHT from the fish. The result is that the fish does not APPEAR to be at that place where it really is.
First we have to calculate the time taken to travel the distance 30 m, is
.
Now from equation of motion,
Given, 
.
As object starts from rest, so u = 0.
Substituting these values in above equation, we get
.
Thus, the acceleration is 
