Your answer is C. m∠RCD = m∠ACD ÷ 2.
We know this as we are told that CR is perpendicular to AB, and therefore m∠RCD must be 90°. Then, m∠ACD is 180°, as points A, C, and D all lie on a straight line and angles in a straight line add to 180°. Thus, we know that 180 ÷ 2 = 90, and so m∠ACD ÷ 2 = m∠RCD.
I hope this helps!
