Complex sentence: The school has some 800 pupils from more than 55 countries, 60% of whom are U.S. citizens, and is composed of five campuses in West Los Angeles, Palms and the Pacific Palisades.
Split into simpler sentences: The school has some 800 pupils form more than 55 countries, 60% of whom are U.S. citizens. It is composed of five campuses in West Los Angeles, Palms and the Pacific Palisades.