Your error is pretty clear. Leprechaun does not contain a method called findTreasure. In your leprechaun class you have the following methods
public void chooseTreasurePail
public void chooseTreasureChest
public void choosePatti
public String getGreeting
public double getAssetValue
public int meetPerson
There is no findTreasure method in your Leprechaun class. If you were to add
public void findTreasure(Treasure yourparam)
Then your error should go away.