Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

Problem: on a certain transatlantic crossing, 30 percent of a ship ' s passengers held round - trip tickets and also took their cars abroad the ship. if 60 percent of the passengers with round - trip tickets did not take their cars abroad the ship, what percent of the ship ' s passengers held round - trip tickets ?
Options: a. 33.3 %, b. 40 %, c. 50 %, d. 60 %, e. 75 %
e