Taking the center of the wheel to be the origin, the positive y- axis upward, the positive x- axis to the right, and one foot as the unit in both x and y directions, the equation of the wheel is . The ground is 72 feet below the center of the wheel so it is y= -72. 100 feet above the ground is y= 100- 72= 28. What is x when y= 28? There are two answers to that but both give the same distance from base.