How do I solve a diameter

If you have a radius, which is half of a diameter, then multiply the radius by 2.

The diameter of what i hpe its a circle because if so then The radius is the distance from the center of the circle to its edge. For example, if the radius of the circle is 4 cm, then the diameter of the circle is 4 cm x 2, or 8 cm. If you know the circumference of the circle, divide it by π to get the diameter.