Depreciation

Hi Mr John. The carrying value of a company's non-current assets was 200,000 at 1 August 20X0.During the year ended 31 July 20X1, the company sold non-current assets for 25,000 on which it made a loss of 5000.The depreciation charge for the year was 20,000.What was the carrying value of non-current assets at 31 July 20X1? Like you explained in the lecture, In terms of Dispoal Account on debit side I should put in cost of asset and credit side cash for sale and depreciation.....So the question is how do I know what part of whole depreciation charge(20,000) belongs to the asset I'm selling.... I find it very confusing....Thank you..