Ignored white space

1

I’m NEW to php. I am working my way through a text book, and came upon a problem. I understood white space was ignored in PHP, yet in line 4 of the following code, if I eliminate the white space on either side of “$distance / 10”, the page doesn’t work. can someone explain why, so i might be able to avoid this problem in the future.

Thanks

while ($distance <= 250)
{
echo "<tr>
 <td align='right'>$distance</td>
";
echo "  <td align = 'right'> ". $distance / 10 ." </td>
</tr>
";
$distance += 50;
}