A group of friends charters a boat for \(\$540,\) and each person contributes equally to the cost. They determine that

A group of friends charters a boat for \(\$540,\) and each person contributes equally to the cost. They determine that if they can get three more of their friends to join them, every person in the group will pay \(\$9\) less. If they find three more friends to join them, what is the total number of people renting the boat?

(A) \(6\)
(B) \(9\)
(C) \(15\)
(D) \(18\)
(E) \(21\)

[spoiler]OA=C[/spoiler]

Source: Manhattan GMAT