The file P14_35.xlsx contains the amount of money spent advertising a product (in thousands of dollars) and the number of units sold (in millions) for eight months.

a. Assume that the only factor influencing monthly sales is advertising. Fit the following two curves to these data: linear (Y = a + bX) and power (Y = aX^b). Which equation best fits the data?

b. Interpret the best-fitting equation.