how would you share a variable between 2 classes?

[David24]

i'm trying to share the variable: target

This section of code:

            //draw rectangles for the edges filter
            if( coordinateList.CalculateEdges().Length > 0 )
            {
                using( Graphics graphics = Graphics.FromImage( newImage ) )
                {
                    graphics.DrawRectangles(
                        new Pen( Color.Blue, 1 ),
                        coordinateList.CalculateEdges());
                    //code i added to display 'target'
                    graphics.DrawRectangle(
                        new Pen(Color.Red, 2), target);
                }
            }

Is in the ImageProcessing class and this;

                if (coordinateList.Count != 0)
                {
 
                    int x1 = 0;
                    foreach (PointOfInterest p in coordinateList)
                    {
                        x1 += p.XCoordinate;
                    }
                    double aX = x1 / coordinateList.Count;
                    
                    int y1 = 0;
                    foreach (PointOfInterest p in coordinateList)
                    {

                        y1 += p.YCoordinate;

                    }

                    double aY = y1 / coordinateList.Count;

                    int x = (int)Math.Round(aX, 0);

                    int y = (int)Math.Round(aY, 0);
                    PointOfInterest target = new PointOfInterest(x, y);

                    coordinateList.Add(target);

                }

is in the CoordinateList inner-class. I could never get classes to share a variable..It’s as if I need a global variable but C# of course doesn’t use them plus it would be considered bad OOP.