Two chords KV and QR of circle O are perpendicular at point P, with PQ=6 and PR=8 If radius of circle is sq root of 65. find KP and PV.

The answer is KP=12 and PV=4

My ques is how did they get KP? i understand how they get PV since QP*PR=KP*PV

But i dont know what to do with the radius to get KP?