I got that one ‘wrong’ too. Ugly construction of question, not entirely correct, and very outdated. The rationale is to connect all the adjectives that describe the noun ‘train pass’. Which contains another adjective - ‘train’. So why didn’t they hyphenate ‘train’ and ‘pass’? I wouldn’t call their ‘correct’ choice as normal usage here in Aus. Maybe hyphenate ‘twenty-four’ cos this functions as a single word but the ‘hour’ surely doesn’t need it for clarity any more than ‘train-pass’ does. Bad question really.