A certain project has three activities on its critical path. Activity A's normal completion time is five days. It can be crashed to three days at a cost of $500. Activity B's normal completion time is six days, and it can be crashed to four days at a cost of $50. Activity C's normal completion time is eight days. It can be crashed to three days at a cost of $1,000. Which activity should the project manager crash and by how many days? How much will it cost?