The area of a rectangle is 72 square inches and its perimeter is 36 inches. Find its dimensions.
so, which two factors of 72 add up to 18?
1 72
2 36
3 24
4 18
6 12 <--- we have a winner!
or, you can do the algebra
xy = 72
2(x+y) = 36
.......................
x + 72/x = 18
x^2 - 18x + 72 = 0
(x-6)(x-12) = 0