Determine which activities should be crashed and the total cost of crashing if the goal is to ...

Here is a list of activity times for a project as well as crashing costs for its activities. Determine which activities should be crashed and the total cost of crashing if the goal is to shorten the project by three weeks as cheaply as possible. There are three paths (top, middle and bottom). Each path contains three sequential activities which must be performed in the order they are listed (e.g., A before B, B before C). Note that Activity C is contained on both the top and middle paths.

  Path   Activity   Duration (weeks)   First Crash   Second Crash
  Top   A                         5                   $8                $10             
            B                         6                     7                   9             
            C                         3                    14                  15             
  Middle   D                         3                     9                  11             
            E                         7                     8                   9             
            C                         3                    14                  15             
  Bottom   F                         5                    10                  15             
            G                         5                    11                  13             
            H                         5                    12                  14   

                             
                            Activity                     Cost

First crash    G, B, or F?           $_____?
         
Second crash    A-C, D-E, or B-G?   $_____?
         
Third crash   C-H, B-E, or F-G?    $_____?