Capital Budgeting

A machine owned by a company has been idle for some months but could now be used on a one year contract which is under consideration. The net book value of the machine is $1,000. If not used on this contract, the machine could be sold now for a net amount of $1,200. After use on the contract, the machine would have no saleable value and the cost of disposing of it in one year’s time would be $800.
What is the total relevant cost of the machine to the contract?
A $400
B $800
C $1,200
D $2,000

My answer)- Sir I used the answer as B which is apparently wrong

This was my thought process
They asked the relevant cost for the contract so I assumed that they they do not want anything to do for the disposal ‘not used on contract’

So I checked the answers later and it was wrong so then I realized that incremental costs are relevant costs which are changes in cost or revenues that happen from a direct result of a decision to invest

So then I assumed that the oppurtunity cost of not disposing without the contract will be the incremental cost for the contract

Therefore the 1200 will added with 800 and you get 2000

Sir this is how I assumed the answer was supposed to be
I’m not sure whether my appproach of assuming 1200 as the oppurtunity cost(hence incremental cost) was corrrect

Please correct me if I’m wrong with the approacch sir