21. (a) A small project consists of seven activities for which the relevant data are given below. Activity A Preceding activity Activity duration in weeks 4 B 7 C 6 D A, B 5 E A, B 7 F C, D, E G C, D, E 6 5 5 (i) Draw a network for the above project (ii) Find the completion time for the project. (b) Use the data in the table below to draw a PERT network diagram. Activity Precedence A Activity durations (weeks) Most likely (Realistic) time (m) Optimistic time Pessimistic time (a) (b) 6 8 B 3 4 5 C A 2 3 3 D B 3.5 4 5 E B 1 3. 4 F - 8 10 15 G E, F 2 3 4 H C, D 2 2 2