Basic caculation in info field Kirby

The CMS Questions
1

I’m trying to perform calculations on the front-end of my Kirby website with php, it’s working well so far. <p><?= round(($ServicesTotalCost + $FeesTotalCost) * 0.40) ?><?= $page->currency() ?></p>

I ultimately want to store this calculated value in the Kirby back-end as a field so I can use it later. I’m unsure if the fileMethods approach is best for this purpose since I’m not manipulating a file.**

As simple as it seems, I’m not even able to display a simple test string in the info field…

My info field

fields:
  info:
    label: Total
    type: info
    text: "{{ getLink }}"

index.php of my plugin

<?php
Kirby::plugin('conv/CV', [
	'fileMethods' => [
		'getLink' => function () {

			return 'test';
		}
	],
]);
2

A file method needs to be called on a file object, so file.getLink, but that would only make sense if you are in the context of a file. Where are you using this info field?