Problem 2-8.

The horse's trip is divided into two parts. The first part is to travel away from the trainer (+ velocity) to 130m in 14s. The second part is to gallop halfway back (- velocity).

Note that even though the horse was traveling towards the trainer and the velocity was negative at the last part of the trip, the average velocity of the whole trip was still positive (the horse traveled too far away from the trainer at the beginning).