3 12 fraction minus 8 12

If you are saying:

(3/12) - (8/12)

Then since their denominators are the same we can subtract the numerators to get our answers.

3 - 8 = - 5

Following the rule of adding and subtracting fractions, the denominators will not change unless they are different.

So: (3/12) - (8/12) = - 5/12