Simplify the following text for a Grade 6 native English-speaking person.
Original: During his tenure , the Philharmonic enjoyed a period of unprecedented success and prosperity and performed its first world premiere written by a world-renowned composer in the United States â `` AntonÃ n DvoÅ Ã k 's Ninth Symphony `` From the New World '' .
Simplified: He gave the first performance of AntonÃ n DvoÅ Ã k 's Ninth Symphony `` From the New World . ''