Revision of Future Tax Rates example

the textbook provides the following example. I am confused by an aspect of it and am looking for further explanation.

Assume that on December 10, 2020, a new income tax act is signed into law that lowers the corporate tax rate from 40% to 20%, effective January 1, 2022. If Hostel co. has one temporary difference at the beginning of 2020 related to $3 million of excess tax depreciation, then it has a Deferred Tax Liability account with a balance of $1,200,000 ($3,000,000 X .40) at January 1, 2020. If taxable amounts related to this difference are scheduled to occur equally in 2021, 2022, and 2023, the deferred tax liability at the end of 2020 is $1,100,000 as computed below

	2021	2022	2023	Total
Future Taxable Amounts	$1,000,000	$1,000,000	$1,000,000	$3,000,000
Tax Rate	40%	20%	20%
Deferred Tax Liability	$400,000	$200,000	$200,000	$800,000

I have italicized and bolded the part that I do not understand. How does the deferred tax liability become $1,100,000 at the end of 2020? As far as I understand, it is not shown in the chart, and I cannot seem to figure out how it goes from $1,200,000 to $1,100,000. As far as I understand, the deferred tax liability becomes $800,000.

Please help me understand why I am incorrect in my thinking, and provide the calculations for how the deferred tax liability decreases by $100,000 from the beginning of 2020 to the end (the year which I presume is the originating temporary difference).

Thank you!