Question: In the diagram below, $\overline{P S}$ is a tangent to circle $O$ at point $S, \overline{P Q R}$ is a secant, $P S=x, P Q=3$, and $P R=x+18$.What is the length of $\overline{P S}$ ? A) 6 B) 9 C) 3 D) 27. Please choose an answer from [A, B, C, D].
Answer: B