Look at the initial position of the circle and the straight line on the graph. You can see that they cross in two places. What are the coordinates of the points where they cross, and how does that tie in with the solution of the two simultaneous equations at the right of the screen?
Look at that equations carefully.

They can be solved by substituting for x or y and then solving a quadratic equation.
You can vary the straight line graph by clicking A+, A-, B+, B-, C+ and C-. You can vary the radius of the circle by clicking Radius+ or Radius-.
Go ahead. Try it. Are there always solutions? How many? Sometimes only one? Investigate!