The city has stopped a Manhattan prep school from selling an affordable housing complex to a private condo developer. The 199-unit Trinity House at 100 West 92nd Street is the last Mitchell-Lama building in the Upper West Side. The Department of Housing, Preservation and Development said the high pending sale price, estimated at more than $30 million, made it clear that the buyer would not be able to charge affordable rents and recoup its investment. Tenants are trying to purchase the building themselves or find a nonprofit developer to do so. The Real Deal reported on the tenants’ efforts to buy the building in January.