E2 OT Exam Critical Path

Hi I am soon to sit my E2 OT exam and in one of my online mock exams it asks you to work the Critical path and activity slack for projects on the computer. Can anyone advise how you can do this without the use of a pen and paper? I tried my best at laying it out by thought process but couldn't do it. Is there a simple way of working this out just by looking at the table of activities and duration of each?

Thanks