Answer:
The radius is: 
Step-by-step explanation:
The equation of a circle in center-radius form is:

Where the center is at the point (h, k) and the radius is "r".
So, given the equation of the circle:

You can identify that:

Then, solving for "r", you get that the radius of this circle is:

A radioactive atmosphere around the area and an expensive, hard time cleaning everything up.
7x4x100=2800
7x4x1000=28,000