Question 1121809
The distance between two points (numbers), a and b, on a number line is  |a-b| <br>

In the example you provided,  {{{ abs( b - (-2.6) )  <= 0.4 }}}  —>  {{{ abs(b+2.6) <= 0.4 }}} <br>

In the problem you posted,  {{{ highlight(  abs(b - 4.1) <= 1.2 ) }}}  <br>

Also, notice that [ ]  indicates "includes endpoint(s)" (also known as a closed interval) and 
 ( ) indicates "does not include endpoint(s)" (also known as an open interval)
and if you see one of each, that  indicates a half-open interval.