can someone please help explain this?? if anyone knows an excel formula that would help alot too.

Dave Fletcher was able to determine the activity times for constructing his laser scanning machine Fletcher would like to determine ES EF, LS, LF and slack for each activity. The total project completion time and the critical path should also be determined. Here are the activity times: Time Activity (weeks) A 5 B 8 3 D 2 Immediate Time Predecessor(s) Activity (weeks) E 4 F 5 G 11 A H 8 Immediate Predecessor(s) B B C.E D.F Dave's earliest start (ES) and earliest finish (EF) are ES EF Activity A B 5 00 0 8 D 5 m 12 F 8 G 23 H 21 Dave's latest start (LS) and latest finish (LF) are: Dave's latest start (LS) and latest finish (LF) are: LF Activity H LS 15 G 12 F 10 E 8 D 13 9 B 0 4 The slack times are: Slack Activity A B C E F E 8 D 13 C 9 B 0 A 4 The slack times are: Slack Activity B G H The activities on the critical path are The total project completion time for Dave = weeks. Time Ramai A A-D-H A-C-G B-F-H B - E - G the critical path are