I need to find the most cost-efficient solution for the problem. The network diagram for this question is provided for your reference only. Please explain step by step so I can learn. Thank you!

Early Late Early Late Early - Late Late Weekly Weekly Cumulative Cumulative Cumulative Weekly Early Start Start Week Expense Expense Expense Expense Expense Activity Successors Duration Cost A,B,C B 10 1 60 20 60 20 40 A D B,C,D B 90 20 150 40 110 B E,F 20 W N C,D,E, F A, CE 160 90 310 130 180 C 30 D,E,F,G 190 500 D 40 LIIQ D,E,F,G 190 690 50 WNODADAWN E, F,G 150 340 40 E,G 110 950 G 60 G,H 8 120 1070 H 60 G , H 120 1 190 20 H, I 10 80 1270 J none 30 H,I 11 80 1350 H 12 60 1410 13 60 1470 14 30 1500 30 1530 30 1560 A=1 D-4 H=6 O O O O E=5 B=2 O F-4 J=3 O C=3 G=6 1=2