Answer:
If the diameter is 30 cm, the radius is 15 cm
Explanation:
What is the diameter of a circle?
It's a straight line that runs from one side of the perimeter through the center to the other side of the perimeter.
The hint is exactly correct, the radius is a half of the diameter, or the diameter is 2 times the radius.
If the diameter is 30cm, the measure of the radius is 30 ÷ 2 ( = 15)