How much metal is required to make a 20 metre long pipe, if its inner

1.	How much metal is required to make a 20 metre long pipe, if its inner and outer diameter are 6 metre and 8 metre respectively.
Answer» $\underline {\pink{ Dimensions \: of \: a \: metal \:pipe : }}$ $Length \:of \:the \: pipe (h) = 20 \:m$ $Inner \: Diameter (d) = 6 \:m$ $Inner \: radius (r) = \frac{d}{2}$ $= \frac{6}{2}$ $= 3 \: m$ $Outer \: Diameter (D) = 8\:m$ $Outer \: radius (R) = \frac{D}{2}$ $= \frac{8}{2}$ $= 4 \: m$ $\red{ Metal \: required \: to \: make \:the \:pipe }$ $= \pi h ( R^{2} - r^{2} )$ $= \pi h ( R + r )( R - r )$ $= \frac{22}{7} \times 20 \times ( 4 + 3 )( 4 - 3 )$ $= \frac{22}{7} \times 20 \times 7 \times 1$ $= 22\times 20$ $= 440 \: m^{3}$ •••♪