Correct : 4

Network Paths and Their Durations
A → B → D → G → H = 4 + 8 + 2 + 3 + 9 = 26 hours
A → B → E → H = 4 + 8 + 7 + 9 = 28 hours
A → C → F → H = 4 + 5 + 6 + 9 = 24 hours

Critical Path
Longest path is A → B → E → H = 28 hours, so the project duration is 28 hours.

Early Start (ES) and Early Finish (EF) for Activity D
ES of A = 0, EF of A = 0 + 4 = 4
ES of B = 4, EF of B = 4 + 8 = 12
ES of D = 12, EF of D = 12 + 2 = 14

Late Finish (LF) and Late Start (LS) for Activity D
LF of H = 28, LS of H = 28 − 9 = 19
LF of G = 19, LS of G = 19 − 3 = 16
LF of D = 16, LS of D = 16 − 2 = 14

Slack Calculation for Activity D
Slack = LS − ES = 14 − 10 = 4 hours
Slack = LF − EF = 16 − 12 = 4 hours

✅ Slack for Activity D = 4 hours

Note: Slack of 0 means the activity lies on the critical path. A slack of 4 means Activity D can be delayed up to 4 hours without affecting the overall project deadline.