For the relevant cost data listed below, indicate which is the best classification:

Sunk cost; incremental cost; variable cost; fixed cost; semi$-$variable cost; controllable cost; non$-$controllable cost; opportunity cost

$($a$)$ A company is considering selling old equipment that has a book value of $R10000.$ In evaluating the decision to sell the equipment, the R$10000$ is a $...$

$($b$)$ As an alternative to the old equipment, the company can rent a new machine. It will cost R$3000$ per annum. In analysing the cost behaviour, the rental is a $...$

$($c$)$ To run the company's equipment, the operator could be paid a basic salary plus an additional amount per unit produced. The total salary payable to the operator would be a $...$

$($d$)$ If the company wishes to continue using the equipment, it needs to be repaired. For the decision to retain the equipment, the repair cost is a $...$

$($e$)$ The old equipment mentioned in $($a$)$ could be sold for R$8000.$ If the company decides to retain and use it$,$ the $R8000$ is a $...$

$($f$)$ The equipment is charged to each department at a rate of R$3000$ per annum. In evaluating the performance of the departmental manager, the charge is a $...$