Answer: Option B
Internal radius :
$$\eqalign{
& = \left( {\frac{{11.2}}{2}} \right)cm \cr
& = 5.6\,cm \cr} $$
External radius :
$$\eqalign{
& = \left( {5.6 + 0.4} \right)cm \cr
& = 6\,cm \cr} $$
Volume of metal :
$$\eqalign{
& = \left[ {\frac{{22}}{7} \times \left\{ {{{\left( 6 \right)}^2} - {{\left( {5.6} \right)}^2}} \right\} \times 21} \right]c{m^3} \cr
& = \left( {66 \times 11.6 \times 0.4} \right)c{m^3} \cr
& = 306.24\,c{m^3} \cr} $$