Points H and F lie on circle C. Circle C is shown. Line segments E C, F C, and D C are radii. Tangents E G and D G intersect at point D outside of the circle. A line is drawn to connect points F and G. The length of G E is 12 and the length of E C is 9. Angles E and D are right angles. What is the length of line segment GH? 3 units 4 units 5 units 6 units