US mortgage costs continued to ease, with the average 30-year fixed rate falling to 6.63% in the week ended Aug. 7, according to Freddie Mac’s Primary Mortgage Market Survey. The reading, down from 6.72% a week earlier, marks the lowest level since the week of Apr. 10 and extends a three-week slide. Rates on 15-year fixed loans slipped to 5.75% from 5.85%. The drop comes as Treasury yields retreat amid signs of a cooling labor market, broadening home-buying power. Brokerage Redfin said the annual income required to purchase a typical US home has declined year on year in 11 large metropolitan areas, most of them in Sun Belt markets where prices have begun to moderate.