In 1982, Martina Navratilova became the first to win over $1,000,000 in a single year. Navratilovas single year earnings exceeded $2 million in 1984.  In 1997, Martina Hingis became the first to earn over $3 million during a single year.  In 2003, Kim Clijsters surpassed $4 million in earnings for a single year. In 2006, Venus Williams and the WTA pushed for equal prize money at both the French Open and The Championships, Wimbledon.  Both of these Grand Slam (tennis) events relented in 2007 and awarded equal money for the first time.  This enabled Justine Henin, who won the French Open in 2007, to earn over $5 million that year, becoming the first woman in sports to do this. In 2009, Serena Williams went over the six million mark by earning over $6.5 million in a single year. Then in 2012 both Serena Williams and Victoria Azarenka became first players to exceed $7 million in prize money in a single season. In 2013 Serena Williams went over the twelve million dollar mark winning $12,385,572 in a single year. By virtue of winning the 2014 US Open (tennis) and the 2014 US Open series, Serena Williams had the largest payday in the history of tennis (men or women) at four million dollars. Additionally, Serena Williams has won the most Grand Slams (23 as of 2017) in the Open era, beating out tennis legend, Steffi Graf. Serena is only one behind Margaret Court for total singles titles in womens tennis. Her career prize money of $84 million is more than twice as much as any other female athletes.

How many years after Navratilova set a record for earning $1 million in one season did Hingis earn $3 million in one season?
15