How many different three-digit numbers can be formed by using the three numbers 3, 7, and 9 to form a three-digit number?
用3、7和9这三个数字组三位数，一共可以组成多少个不同的三位数．
<gadget id="calculator">3 * 3 * 3</gadget>
<output>27</output>

<result>27</result>