Perimeter is adding all 4 sides together.
To find the length and width divide total perimeter by 2:
21 / 2 = 10.5
We now know the length of 1 side and the width of 1 side need to equal 10.5.
Since the original piece was a square we also know the width needs to equal 1/2 of the length.
So we have L + 1/2L = 10.5
Add the common terms 1 L + 1/2 L = 1 and 1/2 L
To Find L divide 10.5 by 1-1/2, which equals 7
To find the width subtract 7 from 10.5, which equals 3.5
So the paper is now 3.5 inches by 7 inches.
