(i)Circles touching externally
If the circles touch each other externally, distance between their centres is equal to the sum of their radii.
Distance between the centres = 4+2.8 = 6.8cm
(ii)Circles touching internally
The distance between the centres of the circles touching internally is equal to the difference of their radii.
Distance between the centres = 4-2.8 = 1.2cm