I need help on this question. It keeps telling me the first two answers are wrong, for A and B are wrong

The table below gives the change in the level of an aquifer each month in a given year. The first column gives the month. The second column gives the change in level in feet for that month. The level of the aquifer at the start of the year is 684.1 feet. Month Change in level (ft) 0 0 1.3 12 0.6 3 1.0 4 -1.7 5 -0.4 6 -4.7 42 8 -29 9 -1.2 10 -12.5 11 -1.4 12 5.6 Let L(t) be the water level in feet after t months. Note that the table above gives the values of L'(t) a) Then L(8)= 685.3 feet b) Using these approximations, find the net change in water level during the year. The net change is 121 1 feet c) The highest that the water level reaches during the year is 687 feet d) The water level is lowest at the end of month number 11