A circle is shown. Secants E G and D G intersect at point G outside of the circle. Secant E G intersects the circle at point F and secant D G intersects the circle at point H. The length of E F is x, the length of F G is 6, the length of D H is x + 3, and the length of H G is 5. What is the length of line segment DG? 4 units 7 units 12 units 23 units