construction project

 A construction project is broken down into the following 10 activities: 
Activity Immediate Predecessor Time (weeks)
1 ---- 4
2 1 2
3 1 4
4 1 3
5 2,3 5
6 3 6
7 4 2
8 5 3
9 6,7 5
10 8,9 7
a. Draw the network diagram. 
b. Find the critical path. 
c. If activities 1 and 10 cannot be shortened, but activities 2 through 9 can be shortened to a minimum of one week each at a cost of $ 10,000 per week, which activities would you shorten to cut the project by four weeks?