At the toll booth at the entrance of the expressway, there are four toll windows, No. 1, No. 2, No. 3, No. 4. There are three cars A, B, and C to buy tickets to enter the expressway through the toll window. So, how many different ticket purchase orders are there for these three cars?
高速公路入口处收费站有1号2号3号4号共四个收费窗口，有A，B，C三辆轿车要通过收费窗口购票入高速公路．那么，这三辆轿车共有多少种不同的购票次序．
<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">2 + 2 + 1 + 1</gadget>
<output>6</output>

<gadget id="calculator">4 * 5 * 6</gadget>
<output>120</output>

<result>120</result>