Mr. design is covering rectangular pieces of plywood with fabric to create a wall hanging. each piece has an area of 12 3/4 square inch. one of the rectangles is 2 1/8 inches wide and a second rectangle is 2 1/ 10 inches wide. find the length of each rectangle.

6 inches 
6 1/14 inches  
Since area is defined as length multiplied by width, this is a simple matter of division. I suspect this problem is more a matter of handling fractions, so to make things easier, convert the fractions to improper fractions in order to do the math, then convert to proper fractions after you've gotten the result. Since the area of each rectangle is 12 3/4, multiply 12 by 4 and then add 3 to get 51/4 as the area. Doing the same for the values 2 1/8 and 2 1/10 gives sizes of 17/8 and 21/10 for the widths respectively. So 
 51/4 / 17/8 = 51/4 * 8/17 = 408/68 = 6/1 = 6 
 51/4 / 21/10 = 51/4 * 10/21 = 510/84 = 85/14 = 6 1/14