Help create my plugin random Chest

How to generate a chest on random cordinant?
<?php

namespace chest;

use pocketmine\plugin\PluginBase;
use pocketmine\command\Command;
use pocketmine\command\CommandSender;

class Main extends PluginBase{

public function onEnable(){
$this->getLogger()->info("[Chest]");
}
public function onCommand(CommandSender $sender, Command $command, $label, array $args){
if($cmd->getName() == "chest"){
$x = rand(1,100);
$y = rand(80,100);
$z = rand(1,100);
$sender->getServer()->broadcastMessage("[Chest] create random chest cordinants : ( X -> $x ) ( Y -> $y ) ( Z -> $z ) ")

}

}
}