The area of a rectangle is its length x width.
The perimeter of a rectangle is its length + length + width + width.
Let's have l stand for length and w for width. A will stand for area and P for perimeter. This gives us:
399 = l x w
80 = 2l + 2w We can divide both sides of this equation by 2 to get 40 = l + w.
Now we need to find two numbers whose sum is 40 and product is 399.
Fitting some random numbers in gives us the numbers 19 and 21 for the length and width.
