Can you take a look at the file and see what is on "line 116"? It would help to know the version of PHP in use because it has gone through a few transitional evolution steps over the past few years.

Line 116 reads...
$catResult = mysql("$db", "select * from category ORDER BY name");

The PHP Version in use is 5.4.45

This is not an error, this is a message telling you that you are using an out of date function. You can change this by editing php.ini or adding a statement at the top of your script. I suspect you either upgraded from an earlier version of php or changed the php.ini file etc to show warnings.

Because the version of php you are using is 5 years out of date and you should really be using the mysqli library as mysql isn't supported in php 7.x. It's not a big job as most function names are replaced with similar names eg mysql_query() becomes mysqli_query()

If you want to update your site I'd recommend updating your database commands to use mysqli with your current version of php 5.4 and then move to the latest version of php that you can.

You can change the line to get rid of the error in the meantime to

$catResult = mysql_query($db, "SELECT * FROM `category` ORDER BY 'name'");

but please update to mysqli_query as much as I hate to even put mysql_query in that code I believe you would be mixing mysql and mysqli in the mean time which with throw other errors.

Yes, please update all unpatched non updated software especially PHP, which has over 100 known vulnerabilities in the versions between latest and yours. Being ripe for being cracked is not a good place.