On Monday at 1 p. M., when the ocean's surface was at an elevation of 2.2 feet, Winston went to a surf shop that was 8.2 feet above the ocean's surface. At 7 p. M. When the ocean's surface was at an elevation of -2.4 feet, Winston ate dinner at a restaurant whose deck was 10 feet above the ocean's surface. What was the net change in the elevation of the ocean's surface from 1 p. M. To 7 p. M.?