可以

<?php

class Car {

    public $speed = 0;

    //增加speedUp方法，使speed累加10

    function speedUp() {

        $this -> speed = ($this -> speed + 10); 

        $this -> speed += 10;

        echo $this -> speed + 10;

        echo '<br/>';

        return $this -> speed + 10;

    }

}

$car = new Car();

print_r($car->speedUp());

echo '<br/>';

echo $car -> speedUp();

echo '<br/>';

echo $car->speed;

$this -> speed += 10; 分号写错了！