Question 1011292
Depends on which face area is the x^2-9.  Maybe this face has dimensions (x-9) and (x+9).  


Height could be  {{{(x^6-729)/(x^2-9)}}}.


Look at the numerator.
{{{(x^6-729)=(x^3-27)(x^3+27)}}}.


{{{(x-3)(x^2+3x+9)(x+3)(x^2-3x+9)}}}


The height could be, using that,
{{{((x-3)(x^2+3x+9)(x+3)(x^2-3x+9))/((x-3)(x+3))}}}
{{{highlight((x^2+3+9)(x^2-3x+9))}}}