13. (20 points) Consider the following polynomial p(x) = 2x - 5r + 4r' - r + 12 (a) (7 points) Use the Rational Zero Theorem to list all possible rational zeros of p(r). (b) (7 points) Use Descartes' Rule of Signs to determine all possible numbers of positive and nega- tive real zeros. (c) (6 points) Show that z = -1 and z = 3 are lower and upper bounds, respectively, using the theorem about bounds of zeros