A cube whose side length is 5 is shown below. Let P be on edge AB such that AP = 2, and let Q be on edge AE such that
AQ = 1.
The plane passing through points C, P, and Q intersects DH at R. Find the length DR.
This has been asked here before: https://web2.0calc.com/questions/cube-question-help, but the answer can't be seen because tinypic doesn't work, and I don't really think coordinate geo was meant for this problem.
Thanks in advance for your help! 
Also, here is a hint: Let the plane through C, P, and Q intersect the extension of DA at S. What can you say about the diagram? Which two-dimensional figures can you work with?
