Use the idea of external costs to explain why some cities have laws against late-night rock concerts

What will be an ideal response?

While many people might like to see a midnight show featuring AC/DC or Creed, many others argue that a rock concert blaring away early in the morning imposes external costs on many nearby residents who do not want to be disturbed late at night. Therefore regulations on the time that music can be "emitted" are common. To the extent that the regulations are motivated by the externality, such regulations increase efficiency.