A circle has radius 10. A chord is drawn 6 units from the center. What is the length of the chord?

The perpendicular from the center to a chord bisects the chord. This makes a right triangle with hypotenuse $10$ (the radius) and one leg $6$ (the distance to the chord). The other leg is half the chord: $\sqrt{10^2-6^2}=\sqrt{64}=8$. The full chord is $2\cdot8=16$, choice H. Choice F ($8$) is only half the chord. Choice G ($12$) doubles the distance $6$. Choice J ($18$) does not follow from any correct step. The chord must be shorter than the diameter, $20$, and a chord $6$ units from the center is fairly long.