reducing balance and straight line method

John,
in order to calculate the tax allowable deduction for reducing balance, we MUST total cost minus the residual value, then calculate the reducing balance % right ? is that possible the question will ask no need to minus residual value, even it provide the information of residual value

for straight line method, do we need to minus the residual value then divide the total year ? or straight away divide the year ?

another question is, if the question say, the scrap value is 40m in current, however will increase the value per 5 % for each year, when T4, the scrap value will be 48.62m. , in order to calculate the reducing balance, we need to minus 40m or 48.62m for getting the reducing balance amount.

and sometimes the question got mention, the scrap value is post tax , what is that mean ? is that mean we no need calculate the balancing /allowable charge at the cease of the project ?if it is pre tax, then we need to calculate the balancing/allowable charge.

besides sir, do have you any lecturer which are explain more detail in tax treatment in cash flow, in AFM or FM lecture note ? because i want watch it for revision