Activity 7-8 is directly preceded by two activitiesactivity 5-7 and activity 6-7. activity 5-7 has an expected time of five and an es time of six. activity 6-7 has an expected time of seven and an es time of seven. activity 7-8 has an expected time of 10. the es for activity 7-8 is: a) 11b) 14c) 21d) 24e) 25