For her dad, the ending of Joan's whiny behavior is a negative reinforcement and for Joan the cookie is a positive reinforcement.
Step-by-step explanation:
Psychology says that the positive reinforcement means giving something to a person on performing desired action. In simple positive reinforcement is rewarding the person for their action.
Negative reinforcement means strengthening the behavior of the person by avoiding or removing negative outcome.
In the above scenario, Joan was demanding frosted cookie at the bakery. Joan’s father thought that ending of his whiny behavior is a negative reinforcement. But Joan considered cookie as the positive reinforcement.