1. The problem states that RS is the diameter of a circle with center O, and we need to find the value of angle $y$ at point S on the circumference. 2. Important fact: The angle subtended by a diameter at the circumference of a circle is a right angle (90°). 3. Given angles are 116° and 54° at the center O near point R, and angle $y$ at point S on the circumference. 4. Since RS is the diameter, angle $y$ at point S must be 90° by the Thales' theorem. 5. Therefore, the value of $y$ is: $$y = 90^\circ$$ 6. The correct answer is C 90°.