[tex]\begin{gathered} \text{the slant height is 15 and the height is 12} \\ \\ 12^2+r^2=15^2,\text{ because the triangle is right } \\ \\ 144+r^2=225 \\ r^2=225-144 \\ r^2=81 \\ \\ r=\sqrt[]{81} \\ r=9 \\ \\ \text{ the radius is 9} \end{gathered}[/tex]
