SK Networks Co., a trading affiliate of SK Group, said Tuesday it has sold its rental car unit for 820 billion won (US$618 million) to a Singapore-based private equity fund.SK Networks has completed the sale of its 100 percent stake in SK Rent-a-Car Co. to Affinity Equity Partners Ltd., the company said in a regulatory filing."The unit sale is aimed at strengthening the company's financial health and securing capital for investments in future growth businesses," it said.SK Rent-a-Car is South Korea's second-biggest car leasing company after Lotte Rental Co.Source: Yonhap News Agency