Question

what is the length of $overline{qr}$?

Explanation:

Step1: Identify coordinates

The coordinate of point Q is 20 and the coordinate of point R is 60.

Step2: Calculate distance

The distance between two points on a number - line is given by the absolute value of the difference of their coordinates. So, $QR=\vert60 - 20\vert$.
$QR = 40$

Answer:

40