How do you find which activity should be crashed first, the total cost from current duration, and the original duration?

Example:

PM.6B Real estate developer Russell Call was working with a few contractors to make a number of improvements to one of his rental properties. After gathering information from these contractors he determined the following durations, predecessors, and costs of all the required activities: What is the overall duration of the project? Which of the following activities has the lowest crash cost per week? E C D A. Which of the following activities has the highest crash cost per week? C F G B If you wanted to shorten the overall duration of the project, which activity should you crash first? A B C E D What is the total cost of crashing the project from its current duration down to 13 weeks? What is the total cost of crashing the project from its original duration to 11 weeks