So initially your cost is going to be 20-1.4 (residual value) = 18.6m which will be depreciated over 6 yrs:18.6/6=3.1m depreciation per annum YE 08 18.6-3.1=15.5 YE 09 15.5-3.1= 12.4 YE 10 12.4-3.1 = 9.3
now advised that value is 2.6 so difference is now 2.6-1.4 = 1.2m additional value. This you can add to the value of plant so 9.3+1.2 = 10.5. Depreciation has to increase by 0.4 per annum as you have three years left (1.2/3=0.4). Then start depreciating YE 11 10.5 (9.3+1.2) – 3.5 (previous 3.1+additional 0.5).