Normal Crash Normal Crash duration duration cost cost Activity Precedent (days) (days) (PHP) (PHP) A 120 100 12000 14000 B 20 15 1800 2800 C B 40 30 16000 22000 D 30 20 1400 2000 E D 50 40 3600 4800 B 60 45 13500 18000 What is the LF of activity F ? A) 120 ( B) 20 O c) 60 O D) 80 O E) 140