how do you find acceleration?

Question

What is the acceleration of a .4 kg ball from rest to 9 m/s during the .15 s in which her foot is in contact with the ball.

Answer 1

mass doesn't matter here, just the acceleration
v=u+at
a=(v-u)/t
a=(9-0)/0.15=60 m/s^2

Answer 2

a = (v-u)/t
mass here is irrelevant
v= final velocity
u=initial velocity
therefore
a= (9-0)/.15 m/s^2
=60 m/s^2

Answer 3

law of physics...