Final answer:
The prefrontal cortex is the part of the brain where changes occur that help teens regulate their emotions, solve problems effectively, and be more planful in behavior.
Step-by-step explanation:
The changes in the brain that help teens regulate their emotions, solve problems effectively, and be more planful in behavior occur in the prefrontal cortex (PFC), which is the part of the cerebral cortex that covers the front part of the frontal lobes. The PFC is involved in decision making, information processing, abstract reasoning, problem-solving, evaluating risks and rewards, planning ahead, and controlling impulses. It is responsible for the executive functions of the brain, and these functions mature throughout adolescence as the PFC develops.