The sum of Pete's and Sam's ages is 30. Five years ago, Pete was 3 times as old as Sam. How old is Sam? Let P = Pete's age, S = Sam's age, and P + S = 30. Which of the following equations would complete the system?
AP - 5 = 3S
BP - 5 = 3S - 5
CP - 5 = 3S - 15
AP - 5 = 3S
BP - 5 = 3S - 5
CP - 5 = 3S - 15