The perimeter of a rectangle is 99 inches. Its width is 11 inches. Show how to solve for the length algebraically. Then show how to solve for the length arithmetically. Compare and contrast the solution methods. Did you get the same answer using both methods?
99 - 2*11 = 99 - 2*11 = 77
77/2 = 38.5
Perimeter of Rectangle = 2x + 2y where x is the width and y is the length
99 = 2x +2y
99 = 2(11) + 2y
99 - 2(11) = 2y
77/2 = 38.5 = y
You can do the compare and contrast part.
And as you can see they are in fact the same value.