She would have $6.25 because
$8.50
- $ 2.25
_______
Take 5 - 10 = 5 (we have ten because we borrowed, so we have ten remove 1 from 5 you get 4 because we are borrowing)
4 - 2=2 ( we have a four because we borrowed to turn 0 into 10)
Then 8-2=6 (we do not borrow from eight because we already borrowed and there is no need to)
so our final answer is $6. 25
