How many four-digit numbers can be formed using the four numbers 3, 5, 7, and 0? (Numbers are not reused)
用3、5、7、0这四个数字可以组成多少个四位数．(数字不重复使用)
<gadget id="calculator">3 * 3 * 2 * 1</gadget>
<output>18</output>

<result>18</result>