The box and ladder riddle.Place a 1 by 1 meter box (represented by a square on your 2D drawing) on the floor, against the wall (represented by a horizontal and a vertical line say 8 meters long) Place a 5 meter long ladder on the floor and against the wall so that the ladder touches the corner of the box. How high does the ladder reach up the wall? 

It reaches only as high as it has to.

It reaches only as high as it has to??? is it the answer???

not less than 5m.

Maybe I'm missing the point of posting a riddle to a CAD Help site.

There are two answers to this question because of how you can lean the ladder against the box, floor, and wall.  Either the ladder reaches 1.26m above the floor, or 4.84m above the floor.  But John is correct.  This is not a CAD problem  Short of brute force trial and error one can only solve this using algebra and trigonometry.  And even then, it's not a trivial solution.

:) I agree