The x value of the center of the circle is negative, so it should be positive in the equation. That rules out numbers 1 and 3. Also, the number on the right side of the equation should be the square of the radius. That rules out 1 and 2, because the circle can be seen to have a radius of 3, therefore making the number on the right side of the equation equal to 3 squared or 9. This leaves us with equation number 4, which is the correct answer.
