Help me understand this problem especially for the part where I have to pick the least expensive on the critical path .

1. Draw the Activity-on-Node (AON) network diagram Days Cost Cost per Day Activity Predecessor Normal Crash Normal Crash $ Saved/Day A 3 2 $40 $80 $40/Day B A 2 1 $20 $80 $60/Day C A 2 2 $20 $20 D1) A 4 1 $30 $120 $30/Day E2) B W 1 $10 $80 $35/Day 1) Partial crashing allowed. Total Cost = $120 ($40 + $20 + $20 + $30 + $10) 2) Partial crashing NOT allowed. B E A C D 0 1 2 3 4 5 6 7 8 Days2. Pick the least expensive on the critical path activity Days Cost Cost per Day Activity Predecessor Normal Crash Normal Crash S Saved/Day A - 3 2 $40 $80 $40/Day B A 2 1 $20 $80 $60/Day C A 2 2 $20 $20 - DY A 4 1 $30 $120 $30/Day E2) B 3 1 $10 $80 $35/Day 1) Partial crashing allowed. Total Cost = $120 + $40 (A) = $160 2) Partial crashing NOT allowed. 2. Pick the least expensive on the critical path activity Days Cost Cost per Day Activity Predecessor Normal Crash Normal Crash S Saved/Day A - 3 2 $40 $80 $40/Day B A 2 1 $20 $80 $60/Day C A 2 2 $20 $20 - DY A 4 1 $30 $120 $30/Day E2) B 3 1 $10 $80 $35/Day 1) Partial crashing allowed. Total Cost = $160 + $60 (B) = $220 2) Partial crashing NOT allowed. 0 1 2 3 4 5 6 7 8 Days 2. Pick the least expensive on the critical path activity Days Cost Cost per Day Activity Predecessor Normal Crash Normal Crash S Saved/Day A - 3 2 $40 $80 $40/Day B A 2 1 $20 $80 $60/Day C A 2 2 $20 $20 - DY A 42 1 $30 $120 $30/Day E2) B 31 1 $10 $80 $35/Day 1) Partial crashing allowed. Total Cost = $220 + $70 (E) + $60 (D) = $350 2) Partial crashing NOT allowed. 5 0 1 2 3 4 5 6 7 8 Days Reduce the shortest duration. Days Cost Cost per Day Activity Predecessor Normal Crash Normal Crash $ Saved/Day A 3 2 $40 $80 B A 2 1 $20 $80 C A 2 2 $20 $20 D1) A 4 $30 $120 E2) B W 1 $10 $80 1) Partial crashing allowed. 2) Partial crashing NOT allowed