Fluctuation, Inc., recorded the following profit figures in 2011-2013. (10 pts.)

	2013	2012	2011
Net sales	$30,500	$25,600	$22,900
Costs and expenses:
Cost of products sold	$12,600	$10,300	$8,530
Selling	$7,875	$5,205	$4,580
General	$2,950	$2,235	$2,150
Research and development	$4,100	$3,190	$2,840
	$27,525	$20,930	$18,100
Operating income	$2,975	$4,670	$4,800
Other income (expense)	$525	($300)	($400)
Earnings before tax	$3,500	$4,370	$4,400
Income tax	$1,480	$1,990	$2,100
Net income	$2,020	$2,380	$2,300

A. Compute the gross profit margin for each year (6) B. Using plain language, explain what the ratio tells the user and interpret the trend. (4) (Points : 10)