Show how to model the following situations using linear constraints. You may create integer variables when necessary. If you use big$-$M values, be sure to clearly state what the value of M is and how you obtain it$.$

$($a$)|3$x$\_2-$ x$\_1|$ less than or equal to $6.$

Hint: you will not need an integer variable here.

$($b$)|2$x$\_1-5$x$\_2|$ more than or equal to $4,$ where x$\_1$ and x$\_2$ are binary.