3. From the numbers 1 to 15 inclusive, form such pairs of numbers where the difference between the first and second numbers is divisible by 7.
3. Among the numbers from 1 to 15, there are only two that are divisible by 7 - 7 and 14. Now let's form pairs of numbers, the difference of which is 7 or 14.

$$
\begin{array}{lll}
8-1=7 ; & 9-2=7 ; & 10-3=7 \\
11-4=7 ; & 12-5=7 ; & 13-6=7 \\
14-7=7 ; & 15-8=7 ; & 15-1=14
\end{array}
$$

In total, we have nine pairs.

Answer: 8 and 1, 9 and 2, 10 and 3, 11 and 4, 12 and 5, 13 and 6, 14 and 7, 15 and 8, 15 and 1.