Mary has several trees in her back yard. She enjoys them verymuch as they make her back yard very appealing and most importantlythey provide her home with shade which results in lower utilitybills. Mary saves? $300 a year from not having to turn on herair conditioning as often.

?Mary's neighbour, Rachel is fed up with the trees.Come? autumn, leaves fall into? Rachel's back yardcosting Rachel

?$100 to clean up the mess.

What does the Coase Theorem suggest could be a possible solutionto this? problem?