Question 981170
Two things to deal with:
{{{-w^2+36w>0}}} and  {{{2L+2w=72}}}. 


Also knowing that w is width, you can find length information.
{{{A=w(-w+36)}}}.
This means, {{{L=36-w}}}.  Only positive values for L and w are allowed, so this means at least, that {{{w<36}}}.


The roots for area {{{A=-w^2+36=-w(w-36)}}}  are 0 and 36; and A is a parabola which has a maximum and opens downward.


{{{highlight(0<w<36)}}}