The average rate on a 30-year mortgage in the U.S. rose to 6.12% this week, the first increase in seven weeks. The rate ticked up from 6.08% last week, mortgage buyer Freddie Mac said Thursday. A year ago, the rate averaged 7.49%. Last week, the average rate slipped to its lowest level in two years, boosting home shoppers’ purchasing power as they navigate a housing market with prices near all-time highs. Borrowing costs on 15-year fixed-rate mortgages, popular with homeowners seeking to refinance their home loan to a lower rate, rose to 5.25% from 5.16% last week.