Solution:

Given internal diameter of the tube = 11.2 cm

Internal radius, r = d/2 = 11.2/2 = 5.6 cm

Length of the tube, h = 21 cm

Thickness = 0.4 cm

Outer radius, R= 5.6+0.4 = 6 cm

Volume of the metal = R²h- r²h

= h(R²-r²)

= (22/7)×21×(6²-5.6²)

= 66×(6+5.6)(6-5.6)

= 66×11.6×0.4

= 306.24 cm³

Hence the volume of the metal is 306.24 cm³.