The diagram shows a cube of side length 3 inches. The points P, Q, and R have the relative locations shown. P is one of the vertices on the bottom of the cube, Q is located on an edge and is 1 inch from the top of the cube, and R is located on an edge and is 1 inch from the bottom of the cube. If a plane including the points P, Q, and R cuts through the cube, what is the shape of the resulting cross section?​