$P Q R S$ is a square. The midpoint of $P Q$ is $M$ and the midpoint of $R S$ is $N$. If the perimeter of rectangle $P M N S$ is 36 , the area of square $P Q R S$ is
(A) 81
(B) 72
(C) 324
(D) 144
(E) 36

Part B: Each correct answer is worth 6.