Lease & Buy Question

Dear Sir,
I have faced the following example:
Machine cost 20,000$ , useful life 5 yrs and trade-in value 4000$ at the end of the fifth year.
Company could decide to purchase the machine using a loan current rate of interest 13% before tax.
The rate of tax is 30%. If the machine is purchased the company will be able to claim a tax allowable depreciation of 100% in the year 1. Tax is payable with an year’s delay.

Cash flows are discounted at the after tax cost of borrowing so: 13%* (1-0.3)= 9%
Just focusing on purchasing the machine what I did is the following:

Year Cost Discount factor 9% PV
0 20000 1 (20000)
2 6000 0.842 5052 (tax saving, time2 because of tax payable in arrear)
5 4000 0.650 2600 (PV of scrap value at year 5)
NPV= (12348)

However, what should be is the same as above plus this:
Year Bal. Charge Disc. 9% PV
6 4000*30%= (1200) 0.596 (715)

So the NPV is: (12348)+(715)= 13063

Can you please explain me this last calculation? I think that it is related to the tax paid a year’delay but I do not catch the meaning of that. Can you kindly provide me with an explanation of that for a better understanding?
Thanks a lot!
Fede