12. In a marathon competition, the stem-and-leaf plot of the times (in minutes) of 35 athletes is shown in Figure 4\\
\includegraphics[max width=\textwidth, alt={}, center]{a6eae9e4-32c9-40f4-807d-a64508802a24-3_282_990_1347_447}
If the athletes are numbered 1-35 according to their times from best to worst, and 7 people are selected using systematic sampling, then the number of athletes with times in the interval $[139, 151]$ is $\_\_\_\_$.\\