Changing speed of an object

Answer credited to @Asafmen

If it got reduced from a constant speed and they reduced in the other two seconds, by the second t=4 the speed is zero.
That means we need to divide the movement into 4 parts -

1st half: constant speed Vo.

2nd half: speed reduced by negative constant acceleration, a = -1/2 Vo

Why? Since in 2 seconds we went from Vo to 0.

Displacement for the 1st half then can be marked as 2X.

2nd half, X

3X =18


Sections are 6-6-3-0 in terms of how much distance the mobile moved at

The formula is:
1st half,
(Displacement at constant speed)

Second half,
(Displacement at constants acceleration)

When we combine formulas -
D total is 18
Vo is what we want to find
Acceleration- negative half speed
t is 2 (each section is 2sec)

Combine them like on here:

Don’t forget the +1/2 turns to a minus due to negative acceleration.