Let x be the salary. If x is more than the average, we want
![x-34100<2570](https://img.qammunity.org/2020/formulas/mathematics/middle-school/yu7z12q5deqqtjpxs7fbi9e6uv9qufg5iz.png)
If x is less than the average, we want
![34100-x<2570](https://img.qammunity.org/2020/formulas/mathematics/middle-school/fqieqf7qxid3i4d1w9gr5ogbxxn2rjvy5y.png)
The two conditions can be summarized into
![|x-34100|<2570](https://img.qammunity.org/2020/formulas/mathematics/middle-school/9fs4iyu7ec0cqfni06mz6pg71338dr4fmc.png)
In fact, the absolute value of the difference of two numbers tells you "how far" those two numbers are, without taking into account which of the two is bigger.