If a ball starts with the velocity of 2.0m/s and accelerates with a constant rate of 0.50m/s squared for 2.5s what is the balls final velocity

Acceleration can be any change in speed, increasing or decreasing.
You haven't said whether the ball is speeding up or slowing down.

If its acceleration is positive ... speed is increasing ... then in 2.5 seconds,
it GAINS (0.5 m/s² x 2.5 sec) = 2.5 m/s of speed.  Added to its initial
speed of 2.0 m/s, it ends up moving at 4.5 m/s.

If its acceleration is negative ... speed is decreasing ... then in 2.5 seconds,
it LOSES (0.5 m/s² x 2.5 sec) = 2.5 m/s of speed.  Added to its initial
speed of 2.0 m/s, it ends up moving at  -0.5 m/s.  That means that it ends up
moving in the opposite direction compared to its direction at the beginning of
the change.