3. (6 points) Insert two numbers between 2015 and 131 so that the four numbers are arranged in descending order, and the difference between any two adjacent numbers is equal. The sum of the two inserted numbers is

保留源文本的换行和格式，所以翻译结果如下：

3. (6 points) Insert two numbers between 2015 and 131 so that the four numbers are arranged in descending order, and the difference between any two adjacent numbers is equal. The sum of the two inserted numbers is
$$
2146
$$

【Solution】According to the analysis, after inserting two numbers, the sequence forms an arithmetic sequence. Using the properties of an arithmetic sequence, we can find the sum of the two numbers. The sum of the middle two numbers $=2015+131=2146$. Therefore, the answer is: 2146.