Physics questoins about acceleration, motion...?

Question

Hi, please tell me how you would do these questions and the formulas you used to solve these physics

1. A golf club is in contact with a ball for 0.2 sec and imparts a velocity to the ball of 80m/s. Calculate the acceleration of the ball

2. With decelerations, the acceleration is a negative number. A car moves at 20m/s. A child leaps out across a school crossing causing the driver to brake. the brakes deliver 4g's deceleration(4 x -9.8ms-2). Calculate the time to stop after braking

Answer 1

velocity = acceleration * time

1. time = 0.2sec and velocity = 80m/s.  Find acceleration

2. velocity = 20m/s and acceleration = 4*9.8m/s^2, find time.