4. A furniture manufacturer is thinking of adding a new line of waterbeds to its existing line of products. The manufacturer believes it must sell at least 750 beds per month to make any profit. With waterbeds being a new product, sales will probably not amount to more than 10% of the market in the first year. Market research showed the sales of waterbeds for the last 5 years, given in the accompanying table. Apply the least-squares method to predict the demand and to determine whether or not the manufacturer should add the new line. Year Total Sales of Waterbeds per Month 1981 1000 1982 3000 1983 4430 1984 5129 1985 6538