Automatic Conversion To String in PHP

A similar conversion will occur with numbers on which we try to perform an operation allowed only for strings:

php<?php
  $a = 1;
  $b = 2;
  
  echo $a . $b; // outputs '12'
?>

Задание 1

Given three variables:

php<?php
  $a = 1;
  $b = 2;
  $c = 3;
?>

Add the values of these variables as strings.