The equation would be 12(3)+9(1)-50=? Because if she makes 12 skirt that take 3 yards each, you multiply that to know how many yards the skirts take. Then you multiply 9 by 1 to find the yards that the hats use. Then you subtract the those from the total to get what is left over.
12(3)+9(1)-50=? 36+9-50=? 45-50=? The answer is 5 yards left over
