Question 371951
Area of a circle = ðr² 

Inner diameter = 12 cm 
Inner radius = 6 cm 
Outer radius = 6+1 = 7 cm 

Cross sectional area of an annulus (ring) 
= ð(r2²-r1²) 
=(7²-6²)ð 
=13ð cm² 

Volume for a 1 metre tube: 
V=13ð&100cm cm³ 
=1300 cm³ 

Mass ("weight") 
=volume * density.