How do i make a variable?

[jkousholt]

i grabbed this code from admin/themes/default/controllers/products/quantities.tpl

{$available_quantity[$attribute['id_product_attribute']]|htmlentities}

It shows how many of each combination there is for a product.

 

I would like create a variable in modules/mailalerts/mailalerts.php so it can be used in the email $items_table variable 

Like here:

<td style="padding:0.6em 0.4em; text-align:right;">'.Tools::displayPrice($unit_price, $currency, false).'</td>
<td style="padding:0.6em 0.4em; text-align:center;">'.(int)$product['product_quantity'].' (INSERT VARIABLE HERE)</td>
<td style="padding:0.6em 0.4em; text-align:right;">'

Hope it makes sense