Answer:
a) 0 m/s
b) - 24 m/s
c)  - 68 m
Explanation:
Given:
Initial distance = - 4 m
Initial velocity, u = 4 m/s
1) acceleration, a = - 2 m/s² for time, t = 2 seconds
thus, 
velocity after 2 seconds will be
from Newton's equation of motion
v = u + at
v = 4 + (-2) × 2
v = 0 m/s
2) Velocity after 2 second is the initial velocity for this case
given acceleration = - 6 m/s² for 4 seconds
thus,
final velocity, v = 0 + ( - 6 ) × 4 = - 24 m/s 
here the negative sign depicts the velocity in opposite direction to the initial direction of motion
thus, velocity after 6 seconds = - 24 m/s
3) Now, 
Total displacement in 6 seconds 
= Displacement in 2 seconds + Displacement in 4 seconds
From Newton's equation of motion

where,  
s is the distance
u is the initial speed  
a is the acceleration
t is the time
thus, 
=  +
  + 
= - 16 - 48
= - 64 m
Hence, the final displacement = - 64 - 4 = - 68 m