A busy chipmunk runs back and forth along a straight line of acorns that has been set out between its burrow and a nearby tree. At some instant, it moves with a velocity of −1.09 m/s−1.09 m/s . Then, 2.99 s2.99 s later, it moves with a velocity of 1.75 m/s1.75 m/s . What is the chipmunk's average acceleration during the 2.99 s2.99 s time interval