A bakery packs and ships its pies in cardboard boxes. The table below shows the number of boxes remaining in storage at the bakery during a week of 5 workdays.   Boxes Remaining in Storage   Workday Number of Boxes 1 960 2 880 3 800 4 720 5 640 10 560   In the table, the number of boxes, remaining is decreasing at a constant rate each day. What is the slope of the line that graphs the points in the table?