A fisherman in a boat catches a huge fish with a rod and starts to pull it in. The fish
struggles for a while and then becomes still when it is at a distance of 200 m from the
boat. During this operation, the boat (initially at rest) moves 25 m in the direction of the
fish. If the mass of the boat is 5000 kg, calculate the mass of the fish. Assume that water
exerts no friction.