What is the acceleration of a ball traveling horizontally with an initial velocity of 20 meters/second and, 2.0 seconds later, a velocity of 30 meters/second?

The acceleration of the ball is 5 m/s^2.  The formula is: Vf = Vi + at
Vf = final velocity
Vi = initial velocity
a = acceleration
t = time

Substituting the values gives:
30 = 20 + a(2)= 5m/s^2