A simple curve that often makes a good model for the variable cost of a company, as a function of the sales level x has the form y=Pyx+ Box"+ Box". There's no constant term because fixed costs are not included. Complete parts (a) through (c). VA O B. O.C. O D. X Bug . b. Find the least-squares curve of the form above to fit the data (4, 1.55), (6,2.07), (8,2.2), (10,2.9), (12,3.3). (14,3.5), (16,3.9), and (18,4.32), where x and y represent sales and costs in thousands. Produce a graph that shows the data points and the graph of the cubic approximation. (Do not round until the final answer. Then round to six decimal places as needed.)