Which of the following expressions reperesents the distance between -13 and -4 on a number line?

Step-by-step explanation:

You've shared only possible answers a and c.  What about b and d?

Answer a) is correct.  The second - sign represents the difference between -13 and -4 (which is 7, by the way).  -13 - (-4) works out to -13 + 4 = -9, and the absolute value of that is |-9|, or 9, the distance between -13 and -4.