例1某商场购进一批服装(数量足够多),进价为40元/件,以60元/件销售,每天销售20件.根据市场调研,若每件每降1元,则每天销售数量比原来多3件.现商场决定对这批服装开展降价促销活动,每件降价x元(x为正整数).在促销期间,商场要想每天获得最大销售利润,每件降价多少元?每天最大销售毛利润为多少?(注:每件服装销售毛利润指每件服装的销 Example 1 A mall purchased a number of garments (a sufficient number of), purchase price of 40 yuan / piece, to 60 yuan / piece sales, sales of 20 pieces per day. According to market research, if each piece down 1 yuan, the daily sales The number of more than the original 3. Now the mall decided to carry out price cuts on these clothing promotions, each price x (x is a positive integer.) During the promotion, the mall every day to get the maximum sales profit, how much the price of each piece? What is the daily maximum sales gross profit? (Note: The gross profit of each piece of apparel sales refers to the sales of each piece of clothing