Pls help with this question.This question is already discussed in the forum but am not able to follow those answers.

Q:Activity A has a finish - to-finish relationship with activity B. Activity A has a duration of 10 days. activity B has a duration of 9 days with a 3 day lag. what is the total duration of activty a and B?

1.7 days
2.8 days
3.12 days
4. 9 days