1. Find the positive integer $x(0 \leqslant x \leqslant 9)$, such that the tens digit of the product of $\overline{2 x 7}$ and 39 is 9.
1. From $\overline{2 x 7} \times 39=\overline{2 x 7} \times 40-\overline{2 x 7}$, and knowing that the last two digits of $\overline{2 x 7} \times$ 40 are 80, we know that the tens digit of $\overline{2 x 7} \times 39$ is $8-x-1$ or $18-x-1$.
Because $0 \leqslant x \leqslant 9$, so,
$$
17-x=9 \Rightarrow x=8
$$