Here are the solutions needed to answer the qns..For qn 25 part B,it is required of you to understand the system behind the calculation of tax and this include at least a bit of your background knowledge..Fortunately,based on what my Teachers told me,this type of qn is removed from your syllabus as many a times a 16 year-old student cannot relate to tax payment due to their tender age unless you're a working adult/full time worker..FYI,tax is only charged to people who bring back a good basic salary of 25,000 per month and above(of course,not talking about Cpf deduction yet)..Calculating tax on your part now doesn't have any purpose at all..You will most probably not see this qn on your papers nowadays but it's good that you learn something.However don't take my word for everything in case you are tested in future exams..Hope it helps.. :)