CAYLEY 2015 Problem 18

In the diagram, rectangle PQRS has side PQ on the diameter of the semicircle with R and S on the semicircle.

Image

If the diameter of the semicircle is 20 and the length of PQ is 16, then the length of PS is

Answer Choices
A. 6
B. 7
C. 8
D. 9
E. 10