When the velocity of an object is constant, there is no acceleration . Acceleration is defined as a change in velocity over time.
Problem three wants to know if velocity and acceleration have the same signs. I'll assume that on the x-axis the kick goes to the right, that means that velocity has a positive direction therefore positive, acceleration however, is slowing down therefore negative, this is commonly mistaken as deceleration but it's just negative acceleration.
4. when there's constant acceleration, velocity is changing all the time
(constant acceleration would be seen as a parabolic motion where velocity is seen changing at every point.)
you can use the four kinematic equations to find several things like time, distance, and acceleration for the rest