Reliance Industries Ltd said on Monday private equity firm Silver Lake will invest nearly $750 million in its digital arm, days after securing a $5.7 billion investment from Facebook Inc, boosting its efforts to cut debt. The deal adds to a flurry of fund-raising activity announced by the oil-to-telecoms conglomerate in recent weeks including a $7 billion share sale, with plans to eliminate $21.4 billion of net debt by the end of the year.