Calculate early start schedule, late finish, late start and slack

Identify critical path(s).

Where does the assumption of certainty enter into this model? What is the impact of elements being variable?

Activity	Duration	Predecessors
1 Select vendor	1 week	None
2 Hire Finance module consultant	4 weeks	1
3 Hire Materials Mgmt consultant	4 weeks	1
4 Develop internal team	10 weeks	None
5 Select hardware system	3 weeks	2,3
6 Implement hardware system	8 weeks	5
7 Develop Finance interfaces	8 weeks	6
8 Install Finance module	3 weeks	6
9 Test Finance module	2 weeks	7,8
10 Put Finance module on-line	0	9
11 Develop Materials Mgmt interfaces	15 weeks	6
12 Install Materials Mgmt module	6 weeks	10,11
13 Test Materials Mgmt module	3 weeks	12
14 Put Materials Mgmt module on-line	0	13
15 Develop Finance user training	5 weeks	4,7
16 Develop Materials Mgmt user training	7 weeks	4,11

Please show formulas so that I can learn how to calculate LS and slack.