By using R code

Data on last year's sales ( y, in 100,000s of dollars) in 15 sales districts are given in the file sales. This file also contains promotional expenditures(x1, in thousands of dollars), the number of active accounts(x2), the number of competing brands(x3), and the district potential(x4, coded) for each of the districts.

Fit the proposed model in (a) and calculate estimates of i, i=0,1,...,4, and 2.