Position Vector of Reflection of a Point

Hello, I am currently having trouble understanding how to find the reflection point of a point with the coordiantes of that point and the vector equation of the line. I have tried finding the maginitude of the foot of the prependicular, but I still could not get the answer. I hope my doubts can be cleared.

This is the question :

Find the position vector of the image C' of the point C(5,2,-1) under a reflection in the line l joining the points A(3,1,3) and B(-1,-1,-3).