At clock time t = 4 sec, a ball rolling straight down a hill is moving at 5 m/s and is 78 m from the top of the hill, while at clock time t = 9 sec it is moving at 7.5 m/s and is 114 m from the top of the hill.  What is its average velocity during this time?  What is its average acceleration during this time?  Is it possible that the acceleration is uniform?