Philadelphia-based Cigna Corp. reported that it has sold its South African subsidiary to employees and withdrawn from the racially divided country . . . Baker Hughes Inc. reported that the number of oil and gas drilling rigs working in the United States last week increased by 33 to total 1,174. A year ago, the count totaled 910 . . . The Federal Reserve said the average yield for one-year T-bills, the most popular index for making changes in adjustable-rate home mortgages, rose to 6.96% last week after averaging 6.87% the week before.