Here's some quick tips:
--adding "members" means adding variables, like "int purchasePrice",
that's all! :)
--polymorphism is using two different "names" when declaring a
variable, like this: Investment myHouse = new Rental(); See how you
use both "Investment" and "Rental" to create the new variable?
Instead of the usual "String[] bigList = new String[]", which uses the
same name (String) on both sides of the "="
Hope that helps!