Answer is 4.5. Can someone explain the steps to get to the answer?

70) A project is represented by the activity durations (estimated at 90% likelihood of completion) and precedence requirements shown in the table. What is the length of the feeder buffer if this project is managed using critical chain methodology? ActivityPredecessor LengthActivity PredecessorLength 20 DB 200 10FD, E 16 13 70) A project is represented by the activity durations (estimated at 90% likelihood of completion) and precedence requirements shown in the table. What is the length of the feeder buffer if this project is managed using critical chain methodology? ActivityPredecessor LengthActivity PredecessorLength 20 DB 200 10FD, E 16 13