Hi there!
The formula for the perimeter of a rectangle is P = 2 (l + w).
We can simplify this formula so that we can find the solutions easier.
P = 40
40 = 2 (l + w)
divide both sides by 2
40/2 = l + w
20 = l + w
So the length + width has to equal to 20.
So your answers would be B , C , D.
Hope this helped! :)