Tip = bill × tip % ÷ 100, and each person pays (bill + tip) ÷ number of people. A Rs 3,500 bill with a 15% tip adds Rs 525, making Rs 4,025, or about Rs 1,006 each between four people.
Check your bill first, since many restaurants already add a service charge. If not, choose a tip from 5% to 25% to match the service.