SEATTLE (AP) — Microsoft says its affordable-housing initiative has hit upon a model for quickly converting market-rate apartments to ones middle-income workers such as teachers and nurses can afford. The tech giant two years ago announced what is now a $750 million pledge toward increasing the availability of affordable units. As part of that, it said Thursday it has invested $40 million with a partnership called Urban Housing Ventures, which recently bought three apartment complexes in Seattle’s east-side suburbs. The group is cutting rents in 40% of the units for middle-income workers. One resident, middle-school counselor Shanon Baker, said it’s saving her $600 a month and means she won’t have to take a seasonal department store job over the holidays.