The curator of an art exhibit wants to place security guards along the four walls of a large auditorium so that each wall has the same number of guards. Any guard who is placed in a corner can watch the two adjacent walls, but each of the other guards can watch only the wall by which she or he is placed. There is a maximum of one guard per corner. Draw a sketch to show how this can be done with 6 security guards. Show how this can be done for each of the following numbers of security guards: 7, 8, 9, 10, 11, and 12.