A rectangular floor is covered by a rug except for a strip p meters wide along each of the four edges. If the floor is m meters by n meters, what is the area of the rug, in square meters?
mn-p(m+n)
mn-2p(m+n)
mn-p^2
(m-n)(n-p)
(m-2p)(n-2p)
Please explain your answer. Thanks