Complex sentence: Thousands of letters with Halachic issues attached were received at Pumbedita, addressed to the heads of the academy, and from all around the Jewish diaspora, and the Geonim of the academy worked hard to respond to their questions.
Split into simpler sentences: Thousands of letters with Halachic issues attached were received at Pumbedita, addressed to the heads of the academy, and from all around the Jewish diaspora. The Gaonim of the academy worked hard to respond to their questions.