I’ll try and answer this the best as I can.
EXPLANATION: The radius of a circle is the distance from the center of the circle to any point on the circumference.
The easiest way to find the radius is by dividing the diameter in half
1/2 x 11 = 11/2 OR 5.5
ANSWER: the radius of the circle 11 cm in diameter would be 5.5 cm.