I am in desperate need with step by step directions on how to do this critical path model question.

I am in desperate need with step by step directions on how to do this "critical path" model question. I have a test tomorrow and I honestly have no clue where my professor gets these numbers in the circle pie chart step... 

I have the chart with numbers in an attached photo! 

Here is the question: 

Dave Fletcher (see Problem 3.12) was able to determine the activity times for constructing his laser scanning machine. Fletcher would like to determine ES, EF LS, LF and slack for each activity. The total project completion time and the critical path should also be determined. 

(the activity times are in the attached photo.) 

(I also need help how to calculate the critical path)

THANK YOU!