public static function lEquation (T:Dynamic, x1:Float, x2:Float, y0:Float, y1:Float, y2:Float) :Dynamic {
        
        var x0 = (x2 - x1) * (y0 - y1) / (y2 - y1) + x1;
        
        return switch (T) {
            case Int: Math.round ( x0 );
            default : x0;
        }
    }

What is this equation useful? For a lot of things, here's an example how to move a progress bar when you know the percent loaded:

progressBar.width = lEquation (Int, 0, 530, percent, 0, 100);

T is the type you want to return, Int or Float
0 - 530 means that the width of the progressBar will change from 0 to 530 when the percent will take values from 0 to 100

The math:

     ( x0 - x1 )   ( y0 - y1 )
     ----------- = -----------
     ( x2 - x1 )   ( y2 - y1 )

           (x2-x1)*(y0-y1)
     x0 = ----------------- +x1
               (y2-y1)