Answer:
0.56cm
Explanation:
a capillary tube has a cylindrical shape. So we need the formula for the volume of a cylinder:

where
is a constant,

is the radius of the cylinder (the capillary), and
is the length (in this case the length of the mercury thread )
since we need the radius, we solve for it in the last equation:

The information that we already know is:


so we substitue this values:

the radius of the capillary tube is 0.56cm