In drawing A the angles A and d are equal and the hightes point at which 
the ladder could touch the wall is 120 inches if it was standing straight up.


In drawing B the base of the ladder has been moved to the right causing the top of the
ladder to drop lower on the wall.  Lets assign an arbitrary value to X of 117"

Now, using the Pythagorean theorem we can solve for side bc and using trig we 
can find the angle at "a"

Once the distance bc is found we can solve for the angle at "d".  bc minus 24 gives
use the base of triangle edc and we can easily solve for angle d.

So, we know from the illustration A that when angle a and d are equal we will 
know the height of the tip of the ladder as it leans against the wall

All we have to do now is try different values for X until the angles match.  See the
accompaning Excel spresdsheet to see how I did this.

I call htis approach the burte force method.  Marv posted a much more elegant (I think)
solution but that amount of math is beyond me.  Maybe once upon a time I could have
done that but not anymore.

Errol Groff