Complex sentence: Two years later, with all 400 rooms finished, PSA brought in Hyatt Hotels to manage the hotel, which operated from 1974 to 1980 as the Queen Mary Hyatt Hotel.
Split into simpler sentences: Two years later, with all 400 rooms finished, PSA brought in Hyatt Hotels to manage the hotel. It operated the facility from 1974 to 1980 as the Queen Mary Hyatt Hotel.