The Carlyle Group, among the world’s largest investment firms, is looking to sell the stake for Rs 7,000-7,500 crore, valuing Airtel’s data centre unit at Rs 24,000-29,000 crore ($3-3.5 billion, inclusive of debt), the people cited said. Bharti Airtel owns 75.96% of Nxtra Data, a leading player in India’s data centre industry. Airtel has first right of refusal on the stake but is reckoned to have waived it, said the people cited.