WASHINGTON (AP) — Average U.S. long-term mortgage rates fell this week, with the benchmark 30-year loan rate reaching a new low for the year.The rates’ historically low levels could be a boon to potential homebuyers. Mortgage company Freddie Mac says the nationwide average for a 30-year mortgage dropped to 3.80 percent this week from 3.93 percent last week. It is now at its lowest level since May 2013.At the beginning of the year, the 30-year rate stood at 4.53 percent.The average for a 15-year mortgage, a popular choice for people who are refinancing, declined to 3.09 percent from 3.20 percent last week.Mortgage rates often follow the yield on the 10-year Treasury note, which also has fallen to its lowest levels since May 2013.