15.10 The following data represent x=boat sales and y=boat trailer sales from 1995 through 2000.

year

boat sales

boat trailer sales

thousands

thousands

1995649

207

1996619

194

1997596

181

1998576

174

1999585

168

2000574

159

a) determine the least-squares regression line and interpret its slope

b) estimate, for a year during which 500,000 boats are sold, the number of boat trailers that would be sold.

c) what reasons might explain why the number of boat trailers sold per year is less then the number of boats sold per year?