Point C is the circumcenter of triangle PQR. This means that we can draw a circle centered at C that goes through points P, Q and R at the same time. This circle has a special name: circumcircle.
The segments PC, RC and QC are all radii, so they are the same length. Pick two of the given expressions and set them equal to one another. Then solve for x
I'm going to pick the expressions for PC and RC
PC = RC 3x+7 = 5x-15 5x-3x = 7+15 2x = 22 x = 22/2 x = 11
