IRR – Determining Discount Factors

Hello! How do I determine what discount % to use? I get why you would preferably have a positive and negative NPV. The Kaplan books don’t really explain why they’ve chosen the discount factors in the answers. I would normally go 5% and 10% and go from there but Kaplan have used 6% and 10% in an illustration when there was no need to defer from 5%. In the chapter question in the study text, Kaplan used 5% and 12% when they could have used 5% and 10%. Please can someone explain to me why they have done this? It’s wrecking my brain haha