We have two responses for you. Harley thought that by "are" you meant arc and Janice thought you meant area. Take your pick.

Hi Malcolm,

Here are three arcs with the same length but from circles of quite different radii.

Do you know anything else about the arc?

Harley

Hi Malcolm,

I assume you are asking how to find the radius of the area of a circle that is 75 millimeters squared. In order to find what the radius is, we need to manipulate the formula for area of a circle using some basic algebra.

Hope this helps.
Janice