Iam struggling on this physics question. could someone give me the answer to it with a detailed explanation? in advance

question is in the image

Let the big fish’s direction be positive:
m(1)v(1)+m(2)v(2)=m(12)+v(12)

(9.90)(2.00)+(0.10)(-4.00)=(9.90+0.10)v(f)
v(f)=1.94m/s[same direction as big fish]

I believe this is a conservation of momentum question. Because (momentum=mass•velocity), the system, if momentum is conserved, will be (mass of big fish•velocity of big fish+mass of small fish•velocity of small fish=mass of both fish combined+velocity of both fish combined). You add the masses because they are now both travelling as 1 mass. Same with final velocity, they are both one mass so they have to travel together at the same velocity.

B) as the temperature increases, the kinetic energy of the particles increases.|-/