Answer:
1.- Without Retrospective effect
2.- No as it comes from a change in estimations not an accounting error.
3.- yes. It will give a full explanation about the reasons to extend the useful life.
4.- Depreciation expense for 2021: 60,000
Explanation:
1.- The change in the useful life does not represent an accounting error. It comes from the estimation process.
800,000 - 160,000 x 2 = 480,000 book value at beginning 2021
480,000 / 8 new useful life = 60,000 depreciation per year.