depreciation charge clarification

Q: Senakuta Co. purchased a machine with an estimated useful life of 5 years for $34,000 on 30 September 20×5. Senakuta Co. planned to scrap the machine at the end of its useful life and estimated that the scrap value at the purchase date was $4000. On 1 October 20×8, Senakuta revised the scrap value to $2000 due to the decreased value of scrap metal.

what is the depreciation charge for the year ended 30 September 20×9?
a. $7000
b. $6800
c. $2800
d. $6400

Ans: a. $7000
carrying amount at 1.10×8: 34000 – ((34000-4000) x 3/5) = $16000
Revised depreciation charge: (carrying amount – revised residual value / remaining useful life) = (16000 – 2000)/2 = $7000

My doubt is why in carrying amount 34000 is subtracted from the bracket value where already 34000 is specified & subtracted from 4000.
To my understanding, it should be only the bracket value which should give you $18000
i.e. carrying amount at 1.10×8: (34000-4000) x 3/5 = $18000
and then (18000-2000)/2 = giving you $8000 answer?