Question 429099
If the length of a rectangle plus its width is 20cm, then its' length is 20cm minus its width.  Also, we know that the rectangle's total area is 36 sq.cm.. Thus we have:

X(20-X) = 36
20X-X^2 = 36
20X-36 =X^2
0 = X^2-20X+36
0 = (X-18)(X-2)

Thus the dimensions of our rectangle are 18cm X 2cm.