Question 994568
Imagine and draw a circle with center at the origin of cartesian system.  y-axis makes a perpendicular bisector with a chord, and each part of the chord is 3 cm. in length.  Two points on this circle are  (-3,15) and (3,15).


The question asks for the radius of the circle.  How far is  either of the specified  (or found) points from the origina?  That is the radius.
Use the Distance Formula.