Complex sentence: He was a batchmate of Swapan Dasgupta and Paranjoy Guha Thakurta at La Martiniere, and all three went upto St. Stephen's College, Delhi University, after leaving school.
Split into simpler sentences: He was a batchmate of Swapan Dasgupta and Paranjoy Guha Thakurta. Mitra went upto St. Stephen's College, Delhi University, after leaving school.