I am very confused about how to answer those calculation questions, especially when they ask you to prepare in the report format.
Where do I put the detail calculation support in the answer booklet? For example, I calculate all the support before I write the report or I leave a few blank pages and put the calculation at the back
It really depends how much calculation there is. If the calculations are small then include them in the report. If not then best to use the first page (or two if needed) of your answer for the calculations (and head it up appendix). The start a new page with the actual report and refer to the appendix. It does not matter that the appendix comes before the report.