3. a) Let A = {P, Q, R} be the set of nodes in a computer network. Show a communication link relation on set A with 4 links. Each communication link is one directional. Between a pair of nodes, there may be link in one direction, links in both directions, or no links. There may be a loop link at a node. Show the relation in directed graph format and matrix format. b) Show another communication link relation on set A with 8 links. Show the relation in directed graph format and matrix format. 4. a) How many relations are there on the set {a, b}. Show all possible relations on the set {a, b} in directed graph format. b) How many relations are there on the set {a,b,c}. c) How many relations are there on a set with n elements