如何从具有变量的类调用方法？

Given this class:

鉴于此课程:

class Tacobell{

    public function order_taco(){
        echo "3 Tacos, thank you.";
    }

    public function order_burrito(){
        echo "Cheesy bean and rice, please";
    }

}

$lunch = new Tacobell;
$lunch->order_burrito();
$lunch->order_taco();
class Tacobell{