Calculating NPV of option B @ 0% I got 6.4(1-(1+0)^-6)/ln(1+0) and the solution does not exist. The solution has it as 3.84???
You can't really use the annuity formulae with 0% interest as you end up dividing by zero. 0% interest means no interest is applied, so the present value is just the value of payments received. So, 6 years of payments of 0.64 per year is worth 6*0.64 = 3.84
