Banging my head against the wall

Brenna is really testing my patience. Ok, so I don't have any patience left. Sometimes I just don't know how to handle her anymore. She can be so stubborn. Like yesterday. I came home around 6:30, they were playing outside. Fine, asked them if they did their homework. Of course not....why would I expect that hubby actually would remind them? So Sidney sits down and does her homework. Brenna asks me to sit down with her and help her, which I don't mind. So we sit down and she has 3 pages to do for Kindergarten. One is basic subtraction. 3-1=? She tells me the right answer but then proceeds to just fool around on the paper, writes the number the wrong way, erases it, writes it again, erases it, so this goes on a few times. I remind her a couple of times " Brenna, you need to do it nicely, otherwise I will just take it away and you won't get credit for it."

Guess what....yep, I ended up taking it away and she went to school without homework today, which doesn't seem to bother her that much. She was upset last night, but man...........I just lost it, I'm pulling my hair out. Was I ever that stubborn? At that age? Not one of my prouder mommy moments I have to admit. Why can't I just be serene and calm and talk quietly to her? Yeah right.........................