Question:-A closed iron tank 12m long, 9m wide, 4m deep is to be MADE. Determine the cost of iron sheet used at the rate Rs. 5 per m² of sheet.Given DATA :-{ Legth = L; Breadth = B; Depth = D }A closed iron tank 12m long, 9m wide, 4m deep.Cost of iron sheet used at the rate Rs. 5 per m² of sheet.Solution:-Let, 12 m be the length of closed iron tank, 9 m be the breadth of closed iron tank & 4 m be the depth of closed iron tank.Now, we USE FORMULA to find area of a closed iron tank.—› Area of a closed iron tank= 2LB + 2LD+ 2DB—› Area of a closed iron tank= 2×12×9 + 2×12×4 + 2×4×9—› Area of a closed iron tank= 2×12×9 + 2×12×4 + 2×4×9—› Area of a closed iron tank= 216 + 96 + 72—› Area of a closed iron tank= 384 m²The cost of iron sheet used at the rate Rs. 5 per m² of sheet.Hence, —› Cost of iron sheet = [Area of a closed iron tank] × [Cost of iron sheet per m²]—› Cost of iron sheet = 384 × 5—› Cost of iron sheet = Rs 1920Hence, the cost of iron sheet is Rs 1920.