The radius is 7.5 cm
1) Since the Diameter, is an interior straight line segment passing through the origin from side to side, the Diameter is twice longer the radius.
[tex]D=2R\text{ }\Leftrightarrow R=\frac{D}{2}[/tex]
2) As we have in the picture, the Diameter of 15 cm
3) Then we can write
[tex]D=\frac{15}{2}\text{ or D=7.5}[/tex]
