While determining their annual sales data (number of car sales per year) for the past 50 years, a car company found that after taking three successive differences, the resulting data had a mean of 3056 and looked like white noise. If the actual data for the past four years were 2012 - 63214, 2011 - 52874, 2010 - 39981 and 2009 - 35756. What would be a reasonable forecast for sales in 2013? Explain.