Using the four numbers 6, 7, 8, and 9, you can form many four-digit numbers without repeated numbers. Arrange them from small to large, and what is the number 9768?
用6、7、8、9四个数字可以组成许多个没有重复数字的四位数，把它们从小到大排列起来，9768排在第多少个．
<gadget id="calculator">3 * 3 * 2 * 1</gadget>
<output>18</output>

<gadget id="calculator">18 + 3</gadget>
<output>21</output>

<result>21</result>