The time to produce a typical engineering drawing, represented by a random variable X and its quality, represented by a random variable Y. X can be 70, 80, 90 and 100 hours. The quality of drawing can be considered moderate, good and excellent, and Y can be 1, 2 and 3 respectively. If 100 such drawings are evaluated, the following table is constructed: Y\X 1 2 3 70 15 3 5 a) Plot the Joint PMF of X and Y. b) Plot the Marginal PMF of X and Y. 80 90 100 8 3 2 4 6 12 8 12 22 22 c) If only excellent quality drawings are accepted, plot the conditional PMF of X.