Investment Appraisal: using (1+r^x) VERSUS using the annuity factor for NPV calc

Good morning!

Please can you kindly advise how to identify when to use the annuity factor v.s when to use the formula (1+r^x)?

In the following example, the solution multiplies the cost by the annuity factor to find the present value, but goes on to divide the scrap value by (1+r^3), to get the present value please can you help me understand why 2 different methods are used here, and how to know when to use which method?

Example:

A machine will initially cost $540,000, have a life of 3 years, scrap value of $120,000 and annual running costs of $47,000. Cost of capital is 10% – assume all cash flows except the initial cost occur at the end of the relevant year. What is the equivalent annual cost of the machine?

Solution:

Negative NPV ($’000) = ($540 + $47 x 2.487) – ($120 ÷ 1.10^3) = $566.731
Equivalent annual cost = $566.731 ÷ 2.487 = $227.875
Therefore answer = $228,000 to the nearest $’000.

Thank you very much in advance!