Final answer:
The x-coordinate of point A on a circle can be calculated by subtracting or adding the radius from the circle's center x-coordinate, but which operation to use depends on whether point A lies to the left or to the right of the center.
Step-by-step explanation:
To calculate the x-coordinate of point A for a circle named ball, which has been defined with its center's x-coordinate and its radius, one can either subtract or add the radius to the x-coordinate of the center, depending on the specific position of point A. If point A is on the left of the center, we use the x-coordinate of the center minus the radius, which corresponds to option (a) ball.getX() - ball.getRadius(). Conversely, if point A is on the right of the center, we add the radius to the x-coordinate, which is option (b) ball.getX() + ball.getRadius().
Given that the information provided suggests motion in a straight line, this detail alone does not dictate whether point A is to the left or to the right of the center of the ball. To determine which formula to use, one would need additional context about the direction of motion or the specific location of point A in the coordinate system.