in the discounting when cash flow is uneven like in example 3. do we need to calculate the months also by multiplying by 12 or we can leave the answer as 3.79 years
in kit, I saw that they have mentioned the years and months
The discounting (which is only relevant in part (b)) has nothing to do with whether you show the payback period in years or in years and months.
As to whether you need to show the answer as being 3.79 years or as 3 years 9 months will be made clear in the question requirement. Most likely you will be asked to show it as years (so 3.79 years).