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There are  12 units in between. You have to remember the number line is in twos. So, when you count the units in between, you have to remember to count in twos. Another way to figure it out is you can count the number of lines above the numbers or plots and multiply times two to find how many units are in between. Again, multiplying it times two is necessary in this equation because it is in units of two. 

So, there are 12 units in between. 
I really hope this helps and I know how I worded it is kind of confusing, but hopefully you understand. If you have any question feel free to ask. Have an awesome day:)