how to combine variables and text into a string php

<?php
$number = 8;
$txt = "the number is".$number.", ok?"; //Use a dot to combine
echo $txt;
?>

$a = "hello";
$b = "world";
$c = $a . " " . $b;

echo $c; // hello world

Remember dot .

$a = "Hello ";
$a .= "World!";   

public function getAvg(string $var) {
  # A sample from a game I wrote.
  # Concatenatin on the other side is just {stuff.$var}
  # You can also concatenate multiple variables in a varaible:
  # {$varA.$varb}
  $min = $this->{$var._min};
  # Assigns to $min object property matching $var + '_min' string.
  $max = $this->{$var._max};
  # Assigns to $max object property matching $var + '_max' string.
  $avg = (($min + $max) / 2);
  return round($avg);
}