That depends the line
1, If the line is not parallel to Oy, so its equation is y=ax+b
2, Or its equation is x=m
In this question it is given that the values of CD and CE are 20 and 32 respectively.
Since the length of CE is greater then of CD, so C and D could not be the end points.
Therefore, either D and E are the endpoints or C and E are the endpoints.
If D and E are the endpoints, then DE is the sum of 20 and 32 which is 52.
And if C and E are the endpoints, then DE is the difference of CE and CD that is 12.
So the possible values of DE are 12 and 52.
Recall your d = rt. distance = rate * time.
let's say the speed of the current is "c".
keeping in mind that, when the boat is going against the current, the boat is not really going at 2kmh, but instead at " 20 - c ", because the current is subtracting speed from it.
Likewise when is going with the current, is going at a speed of " 20 + c ".
if the boat took say "t" hours on the way over, on the way back it took the slack from the whole 8 hours and "t", namely it took " 8 - t " hours.

Answer:
(a) 100 fishes
(b) t = 10: 483 fishes
t = 20: 999 fishes
t = 30: 1168 fishes
(c)

Step-by-step explanation:
Given


Solving (a): Fishes at t = 0
This gives:






Solving (a): Fishes at t = 10, 20, 30






Solving (c): 
In (b) above.
Notice that as t increases from 10 to 20 to 30, the values of
decreases
This implies that:

So:
The value of P(t) for large values is:



