Final answer:
The best case duration for both activities to finish, given that Activity C has a start-to-start relationship with Activity D and considering the 6-day delay on Activity D, is 21 days.
Step-by-step explanation:
Given that Activity C has a start-to-start relationship with Activity D, the duration of Activity C (12 days) does not necessarily have to be completed before Activity D (15 days) can start. Since Activity D is delayed by 6 days, the best case scenario would be that Activity D starts as soon as Activity C starts, which means they would be running concurrently.
To find the best case duration, we calculate the time it takes for both activities to finish, considering the delay for Activity D:
Since Activity C has a duration of 12 days and Activity D has a duration of 15 days, the duration of both completed (considering the 6-day delay on Activity D) would simply be the longer duration of 15 days plus the delay.
15 days (Activity D duration) + 6 days (delay) = 21 days
Therefore, the best case duration for both activities to finish would be 21 days.