The correct answer to this open question is the following.
Dale works for a publishing company. Every time he writes a good article, he gets lots of fan mail expressing support to him. In the context of operant conditioning, the mails that Dale receives are called positive reinforcement.
B. F. Skinner believed that in order to understand human behavior you have to look to the causes and consequences of any action. He gave a name to this: "operant conditioning." He presented the concept of reinforcement, that serves people to repeat or not an action. He considered that the behavior that is reinforced tends to be repeated and vice versa. That is what Dale is receiving positive reinforcement for the work done.
