The two-step approach:
The rationale: By taking on the tractor, the company (farmer?) has obligated itself to the described cash flows. These are equivalent to an immediate cash outlay of 'X', which you determine in Step 1.
- Determine the NPV of those CFs, using the given discount rate.
- Determine the annual payment of a 5-year annuity which has the same PV. This amount is your "equivalent annual cost".
Instead of an immediate cash outlay of X, the company could opt to borrow X today, thereby swapping the immediate outlay for an obligation on a 5-year fully amortizing note. The annual payment on this note, as you determine in Step 2, is your equivalent annual cost.