Answer :
We have
RT is the diameter
mSO=10
In order to find SA, we will use a trigonometric function
[tex]\begin{gathered} \sin (30)=\frac{SA}{10} \\ SA=\sin (30)\cdot10=5 \end{gathered}[/tex]SM is double of SA
[tex]SM=2(5)=10[/tex]Then using the Pythagorean theorem
[tex]\begin{gathered} OA=\sqrt[]{OS^2-SA^2} \\ OA=\sqrt[]{10^2-(5)^2}=5\sqrt[]{3} \end{gathered}[/tex]