This is a graph of data for the the number of square feet as the independent variable and cost in $thousand for the dependent variable.
Use the PLAY button on the lower right to see the points plotted and the Regression Line drawn. Then note the correlation coefficient, r, and the coefficient of determination, r2, which is computed by geogebra from the data points.
The last point added to the demo is the predictor point P. Click and drag P to see the cost in $ thousands predicted by the regression equation.
www.battaly.com/stat/

What cost does the regression equation predict for a home of 3100 square feet?