The length of the common chord of two circles of radii 15 cm and 20 cm whose centres are 25 cm apart is:

In a circle, two parallel chords of lengths 16 cm and 24 cm are 20 cm apart. Then the radius of the circle is

$\Delta DGH\text{and}\Delta DEF\text{are as shown below.}$ $\text{Find the lengths of segments DG and}\text{DE are \_\_\_\_ respectively.}$
$\text{(All the measures are in cm.)}$

The centres of two circles of radii 3 cm and 2 cm are 8 cm apart. Find the length of the common tangent.