Draw out a number line. Plot -7 and 12 on the number line. Draw in the tickmarks between them. You should find the distance from -7 to 12 is 19 units since you need to go 19 spaces from either -7 to 12, or vice versa.
You can use subtraction to get
-7-12 = -19
or
12-(-7) = 12+7 = 19
The final result is made positive since negative distance does not make sense.
So you'd have |-7-12| = |-19| = 19 or |12-(-7)| = |19| = 19.
All of this only works because the two y coordinates are the same, which makes a horizontal line through the two given points.
