Net book value of asset

Good day to you

A business purchased an asset on 1 January 20X1 at a cost of $160,000. The asset had an expected life of eight years and a residual value of $40,000.
The straight-line method is used to measure depreciation.
The financial year ends on 31 December.
At 31 December 20X3, the estimated remaining life of the asset from that date is now expected to be only three more years, but the residual value is unchanged.

What will be the net book value of the asset as at 31 December 20X3, for inclusion in the statement of financial position?

A 97500
B 100000
C 107500
D 115000

The correct answer was c in the markscheme
In the way I calculated I took (160000-40000)/8
Then I got the answer 150000 depreciation charge
I multiplied 15000*3 to get 45000
And I deducted this from 160000 to get the NBVA

I ignored the fact that the useful life has changed because they state at the end of the year and the useful life will change from originally having 5 years left to 3 years left from the 1/january 2004 and so on…

Since 2004 is next period I assumed that for the year 2003 also the depreciation will be 15000
In other words 2004 change in useful life seemed irrelevant for year end 2003 so I ignored it

In the markscheme however they have apparently already charged a new depreciation for 2003 eventhough it states that in the year end only the useful life is reduced to 3 years

I was wondering why this could be the case