The manager of a store recorded the annual sales 8 (in thousands of dollars) of a product over a period of 7 years, as shown in the table, where fis the time in years, with f: 6 corresponding to 2006. f 6 7 8 9 10 11 12 s 5.4 6.9 11.5 15.5 19.0 22.0 23.6 a. Use the regression features of a graphing calculator to find a model of the form 8 = af3 + bf2 + of + d for the data above. (2 points) b. Use a graphing calculator to plot the data and sketch the model. (2 points) c. Use calculus and the model to find the time twhen sales were increasing at the greatest rate. (4 points) d. Do you think the model would be accurate for predicting future sales? Explain. (2 points)