Can someone me with this and explain how that graph is the answer?

Hello there! So the speed goes up in 6 seconds, maintains for 8 seconds, and then holds for 20 seconds. When something is resting, the line stays straight horizontally for that 20 seconds. B and C are eliminated, because there is no break for C and B does not show the speed accurately. Really, the fish would speed up to 2.5 m/s in 6 seconds, then it maintains that speed, and slows down. D shows a constant speed, which the speed isn't constant, so D is out. A is the only one that represents the scenario properly. The answer is A. 

300b(x) is graphed by the functio