Two different ways to find the difference for 12-3

First, you could count from 3 up to 12 and record the number between them. Second, you could use mental math and try to figure out mentally. The answer is 12-3 = 9

You can either ask "How much is left when you take 3 away from 12?", or you can ask "How far apart are the numbers 12 and 3 on the number line?"

Another way you could think about it is "what number do I have to add to 3 to get to 12?"