Question 758286
I assume that means an 8-cm long piece of pipe, with external and internal diameters 9cm and 5cm respectively, without a cover on either end.
Its volume would be
the volume of a solid cylinder, 8-cm tall, with a diameter of 9 cm,
minus the volume of a solid cylinder, 8-cm tall, with a diameter of 5 cm.
The volume of a cylinder is the area of the base, times the height.
The area of the cicular base is {{{pi}}} times the square of the radius
 
Putting it all together, for a cylinder,
{{{Volume=pi*r^2*h}}}, where
{{{r}}} = radius of the cylinder = {{{diameter/2}}}, and
{{{h}}} = height of the cylinder
 
The volume of the outside cylinder (in {{{cm^3}}}) is {{{pi*(9/2)^2*8}}}.
The volume of the inside cylinder (in {{{cm^3}}}) is {{{pi*(5/2)^2*8}}}.
The volume of the piece of pipe (in {{{cm^3}}}) is
{{{pi*(9/2)^2*8-pi*(5/2)^2*8=((9/2)^2-(5/2)^2)*pi*8=(81/4-25/4)*pi*8=(56/4)*8*pi=112pi}}} = about {{{351.858cm^3}}}.