If the sum of a four-digit number and a three-digit number is 1999, and the two numbers consist of 7 different numbers, how many such four-digit numbers are there?
如果一个四位数与一个三位数的和是1999，并且这两个数由7个不同的数字组成，那么这样的四位数共有多少个．
<gadget id="calculator">8 - 2</gadget>
<output>6</output>

<gadget id="calculator">7 * 6 * 4</gadget>
<output>168</output>

<result>168</result>