You have collected the data for a Time-Cost CPM Scheduling model analysis. The time is in days and the project "direct costs" are given below. The indirect costs for the project are determined on a daily duration basis and are given below: Activity Immediate Predecessor Normal Time (days) Crash Time (days) Normal Cost ($) Crash Cost ($) A None 3 2 300 400 B A 3 3 100 100 C A 1 1 200 200 D B and C 3 2 400 550 E D 2 1 500 900 F E 3 3 200 200 G F 2 2 100 100 Total indirect costs for 16 days of project duration: $ 600 Total indirect costs for 15 days of project duration: $ 400 Total indirect costs for 14 days of project duration: $ 200 Total indirect costs for 13 days of project duration: $ 100 At what project duration do we achieve the lowest total project cost (i.e., direct plus indirect costs)? 16 days 15 days 14 days 13 days