Drawing a circle on a chart

Sample.xlsxHey Guys,

I was wondering if you could help me out with a plotting query:

I have a set of data in eastings and northings (metres). What I wish to do is draw a circle of radius 2100 metres on the graph.

The goal for me is to be able to group all the data points in about 2 or 3 circles. I also need to know the coordinates of the centre point of these circles.

I have attached an example.