Because psychologists generally use college students as research participants, the research does not involve random sampling.
Random sampling is when each sample has an equal chance of being selected. Since the psychologists are targeting a particular set of students, the random sampling might not be applicable in this case.
(c) Only the positive solution makes sense because you cannot have a negative side length. (d) Since one side of the painting is 20 inches, all four sides together will be 20*4 = 80 inches