If a rock layer is found which contains thousands of fossil fish:
A. the fossils piled up as each fish died one at a time
B. the rock layer could have taken thousands of years to form
C. all the fish had to be quickly buried together

most likely A, because rock doesnt just appear, it takes a while to form, therefore the rock layers could have taken thousands of years to form with fish dying in between

can be answered using momentum.

momentum = p

p1= mass1 * velocity1

p1 = p2

therefore

p1 = 6kg * 4m/s

p1 = 24kgm/s

p2=m2 * v2

24 kgm/s = 7kg * v2

v2 = 24 kgm/s / 7kg

v2= 3.42 m/s