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_Given,

_{Dimensions of closed rectangular cistern = 8m × 6m × 2.5 m}

_{∴ Capacity of tank = volume of tank = (l × b × h) = 8 × 6 × 2.5 = 120 m}³

_{Area of iron sheet required to make the tank =} 2(lb + bh + hl) = 2(8 × 6 + 6 × 2.5 + 2.5 × 8)=2(48 + 15 + 20)= 2 × 83 = 166m²