Inline-PHP and Variables not showing

I’m using the Inline-PHP plugin and am creating a template of sorts from an existing page.

I have one section of variables defined so that it is easier to update the pages. My Code looks like this:

[exec]
$category='Canada';
$categoryid='34';
$population='33,992,000';
[/exec]

(html is in here and other layout information)
[exec] echo $population;[/exec] people<p>
Size: [exec]echo $area;[/exec]sq/km</p>

However it does not echo the variables properly. If i place
[exec] $population='33,392,000'; echo $population;[/exec] people<p>

it works just fine, however this sort of defeats the purpose. Is there any other way I can do this to make this work?