Refer to the following information in doing Exercises 19–22. A particularly simple kind of polygon, called a polyomino, is made of squares joined edge-to-edge. The name is a generalization of “domino”; indeed, there is only one kind of domino (two squares joined at an edge to form a rectangle). There are just two trominos (short for “triominos”), the straight tromino and the L-tromino. The straight tromino has the shape of a rectangle, so it can tile the plane by translations; the L-tromino has the shape of a hexagon.