"A company wants to estimate how effective different types of advertising are for promoting its products. Specifically, the company is interested in estimating the effectiveness of radio advertising and newspaper advertising. A sample of 50 cities is selected for the study during a test period of one month. The populations of the selected cities are approximately the same. Each city is allocated a specific expenditure level for radio advertising and for newspaper advertising. Sales of the product (in thousands of dollars) and the levels of expenditure (in thousands of dollars) on both types of advertising are recorded during the test month. The collected data are given

Sales	Radio	Newspaper
2433	0	60
2798	0	60
2188	37.5	37.5
1563	37.5	37.5
2275	45	45
2428	45	45
2328	52.5	52.5
2943	52.5	52.5
2205	60	37.5
2455	60	37.5
4070	67.5	67.5
3943	67.5	67.5
2610	75	0
2285	75	0
3323	82.5	37.5
3325	82.5	37.5
3513	90	45
3590	90	45
3803	97.5	52.5
4353	97.5	52.5
4665	105	60
4293	105	60
1563	37.5	37.5
2275	45	45
2428	45	45
2328	52.5	52.5
2943	52.5	52.5
2205	60	37.5
2455	60	37.5
4070	67.5	67.5
3943	67.5	67.5
2610	75	0
2285	75	0
3323	82.5	37.5
3325	82.5	37.5
3513	90	45
3590	90	45
2610	75	0
2285	75	0
3323	82.5	37.5
3325	82.5	37.5
3513	90	45
3590	90	45
3803	97.5	52.5
4353	97.5	52.5
4665	105	60
4293	105	60
1563	37.5	37.5
2275	45	45
2428	45	45

a.            Specify a suitable multiple regression equation for predicting sales.

b.            Use Excel to estimate the coefficients of the regression equation.

c.             Are the estimated slope coefficients statistically significant? Explain.

d.            Interpret the estimated slope coefficients.

e.            Predict the sales for a city in which radio advertising is $60,000 and newspaper advertising is $60,000.