Answer:
16 4/7
Explanation:
First, you cant subtract 3/7 from 6/7 so take 1 from 19, which turns it to 18. And add that one to 3/7 to get 10/7, or just add 7 to your numerator. So now you have 18 10/7 - 12 6/7. so subtract 18 - 12 to get 6, and the subtract 10/7 - 6/7 to get 4/7. You dont actually have to subtract the denominator just the numerators, because the denominatos are the same so you leave them just the way they are. I hope this helps :)