Answer:
v=u+at is the first equation of motion. In this v=u+at equation, u is initial velocity.
Trial and error
scientific laws and theories are proven by experimental data and large bodies of evidence.
Answer:
average acceleration = 6 
Explanation:
Recall that the average acceleration
is defined by the change in velocity from an initial velocity
, to a final velocity
over the time (t) it took that change to happen. Then, in mathematical terms this is:

with our information this becomes:

Because those layers have been in existence longer than the layer on top of it.