- The rate of depreciation of a building is given by D'(t) = 3000(20 t) dollars per year, 0 ≤ t≤ 20; see the following figure. D'(t) 60 000 50 000 40000 30000 20000 10000 5 10 15 t 20 (a) Use the graph to find the total depreciation of the building over the first 10 years (t = 0 to t = 10). $ 450000 (b) Use the definite integral to find the total depreciation over the first 10 years. $ Need Help? Read It