Pls help me explain how to calculate each row in the table below, I dont understand how to calculate when rate decreases.

Illustration 2 Subsequent change in discount rate The best estimate of the expenditure required is U100 at the end of year 6. The obligation increases by CU 16.67 Le C0100 divided by 6 years), discounted to a current value each year and the initial discount rate is 6%. Subsequently, as a result of a teassessment of prevailing market rates at the beginning of year 4 the discount rate changes to 4%. The expense recognised each period in profit or loss will be as follows: Year 1 2 3 4 5 6 Total 100 100 100 100 100 TOO 6076 5.09 6.096 4,0% 4,096 4.09 Estimated cost of resurfacing Estimated discount tale Opening provision Obligation arising in year (operating cost) Increase prior year provision arising from passage of time finance cost 12.45 26.40 41.98 61.64 80.13 12.45 13.20 13.99 17.98 16.03 16.67 90.32 0.00 0.25 158 168 2.47 3.21 9.68 12:45 26.40 41.98 61.64 80.13 100.00 100.00 Used in year Closing provision 12.45 26.40 (100.00) 0.00 41 98 61.64 80.13 At the beginning of year 4, the discount rate has changed to 4%. The obligation at the end of year 3 was CU41.98. The unwinding of the discount would be the increase in the prior year obligation arising from the passage of time, so an amount of CU1.68 (CU41.98 x 4%) would be charged as a finance cost and the additional amount of CU17.98 (being the net prsent value of the additional 1/6 of the CU 100 provision for the year plus the increase in the provision resulting from the fall in discount rate from 6% to 4%) would increase the provision as an operating item. 47