A rifle bullet, when leaving the barrel, has a velocity of 715 m / s with what acceleration and how long does the bullet

A rifle bullet, when leaving the barrel, has a velocity of 715 m / s with what acceleration and how long does the bullet move into the barrel? its length is 41.5 cm.

SI: 41.5 cm = 0.415 m.
Decision:
Let’s find the average speed:
V = V cf: 2
715: 2 = 357.5 m / s.
Let’s find the time:
t = L: V cp
0.415: 357.5 = 0.001160 s = 1.16 m / s.
Let’s find the acceleration:
a = V: t
715: 0.001160 = 616379.3 m / s2 = 616 km.s2
Answer: t = 1.16 m / s; a = 616 km s2