php basic function return

<?php


function sum($a,$b){
   

$x=$a+$b;

    return $x;
}

$r= sum(411,45);

echo $r;

////////
salida
456
--------------------
<?php


function sum($a,$b){
   

  echo ($a+$b);

   
}

$r= sum(411,45)


////salida  456

------------------------

<?php


function sum($a,$b){
   

  return ($a+$b);

   
}

$r= sum(411,45);
echo $r;

////salida  456




//////////COLOR  OUPUT
<?php

function alert($var) {

if ($var<50) {

$var="<font color=blue>$var</font>";

}


if($var>50) {

$var="<font color=red>$var</font>";


}


return $var;


}

 echo '$var  color  is   '.alert(30);

?>