External diameter = 16 cm.
External radius (R) = 16/2 cm. = 8 cm.
Thickness of sheet = 2 cm.
∴ Inner radius (r) = 8 – 2 = 6 cm.
Height (h) = 100 cm.
∴ Used iron = External Volume – Internal Volume
= πR2h – πr2h
= π (R2 – r2) h
= 22/7 {(8)2 – (6)2} 100
= 22/7 x 28 x 100
= 8800 cm3