MAHow do you apply cost of capital % to this question?

In future, if you want me to answer you must ask in the Ask the Tutor Forum. This forum is for students to help each other. You do not need a calculator to get 4.111 because you are provided with tables in the exam. The inflows for 6 years are an annuity and therefore the discount factor is the 6 year annuity factor at 12%, which from the tables is 4.111. This is all explained in my free lectures on investment appraisal. The lectures are a complete free course for Paper MA and cover everything needed to be able to pass the exam well.