The lines above the number line represent the distance between two values:
Line 1 (upper line)
Starts in -10 and ends in 4
To calculate how much the distance between these two values is you have to subtract the greater value and the smaller one:
4-(-10)=4+10= 14
Line 2 (lower line)
Starts in -10 and ends in 0
The length of this line is
0-(-10)= 0+10 = 10
You can subtract both lines to reach the difference between them:
Line 1 - line 2= 14 - 10 = 4
The difference between the two lines is 4.