You purchased a an apartment building and have your first renter.

Your terms for the apartments are:

Rent is $$2,400$ a month,

Pay up front a $$600$ deposit, and

$1$st and last month's rent.

So the renter has to pay up front, $$7,800.$

Joe Smith comes in to rent an apartment,

He agrees to the terms and pays his $$7,800.$

He travels a lot and does not want to have to keep track of the rent, so he decides to pay