2011 Cayley Problem 22

The top section of an 8 cm by 6 cm rectangular sheet of paper is folded along a straight line so that when the top section lies flat on the bottom section, corner P lies on top of corner R. The length of the crease, in cm, is

\textbf{(A)}\ 6.25\quad \textbf{(B)}\ 7\quad \textbf{(C)}\ 7.5\quad \textbf{(D)}\ 7.4\quad \textbf{(E)}\ 10

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Cayley contests here.