Here is a question about this article: Real estate is a major force in the city's economy, as the total value of all New York City property was assessed at US$914.8 billion for the 2015 fiscal year. The Time Warner Center is the property with the highest-listed market value in the city, at US$1.1 billion in 2006. New York City is home to some of the nation's—and the world's—most valuable real estate. 450 Park Avenue was sold on July 2, 2007 for US$510 million, about $1,589 per square foot ($17,104/m²), breaking the barely month-old record for an American office building of $1,476 per square foot ($15,887/m²) set in the June 2007 sale of 660 Madison Avenue. According to Forbes, in 2014, Manhattan was home to six of the top ten zip codes in the United States by median housing price.
What is the answer to this question: The previous record beaten by Park Avenue was for what real estate?
660 Madison Avenue