A small grocer finds that the monthly sales y (in S) can be approximated as a function of the amount spent advertising on the radio x1 (in S) and the amount spent advertising in the newspaper x2 (in S) according to y = axl + bx2 + c. The table gives the amounts spent in advertising and the corresponding monthly sales for 3 months. Radio Newspaper Monthly sales, y Advertising, x1 Advertising, x2 $2400 $800 $36,000 $2000 $500 $30,000 $3000 $1000 $44,000 a. Use the data to write a system of linear equations to solve for a, b, and c. b. Use a graphing utility to find the reduced row-echelon form of the augmented matrix. c. Write the model y = ax1 + bx2 + C. d. Predict the monthly sales if the grocer spends $2500 advertising on the radio and $500 advertising in the newspaper for a given month.