NEW YORK – The average interest rate on the popular U.S. 30-year fixed-rate mortgage fell to its lowest level since mid-March this week, a welcome development for a housing market struggling to find its footing and one that may continue if the Federal Reserve cuts rates as expected in the months ahead. The 30-year fixed-rate mortgage averaged 6.77% during the week ending July 18, the lowest level since mid-March, down from 6.89% in the prior week, mortgage finance agency Freddie Mac said on Thursday. It averaged 6.78% during the same period a year ago. Data shows that homebuyers are not responding to lowering rates yet with purchase application demand remaining roughly 5% below where it was in the spring, Freddie Mac’s chief economist said.