How can we collect terms?

On Sun, Feb 21, 2010 at 10:21:45PM -0500, thus spake Richard Hennessy:
> You can also use
> 
> expandwrt(your expression, x).
> 

This doesn't work for me.

   Maxima 5.20.1 http://maxima.sourceforge.net
   using Lisp GNU Common Lisp (GCL) GCL 2.6.7 (a.k.a. GCL)

   [...]
                   2  2    2                            2
   (%o7)          m  x  + x  + 2 b m x - 4 m x - 6 x + b  - 4 b + 9
   (%i8) expandwrt(%, x);
                   2  2    2                            2
   (%o8)          m  x  + x  + 2 b m x - 4 m x - 6 x + b  - 4 b + 9
   
Nikos