On a number line what is the distance between −61.5 and -23.4

In order to find the distance between -61.5 and -23.4 on the number line, you just have to subtract either the greater value to lesser value or lesser value to the greater value.  It doesn't matter when you get a negative difference because the distance should be the absolute value of the difference of two points on a number line.
Here's how you should do it.
   (-61.5) - (-23.4) = -61.5 + 23.4 =  l-38.1l = 38.1
or
   (-23.4) - (-61.5) = -23.4 + 61.5 = l38.1l = 38.1

As you can see above, I tried to subtract the two numbers in different order, and the result is still the same. Just make sure to get the absolute value of the answer because the distance should always be in positive form.

Therefore, the distance between -61.5 and -23.4 is 38.1