whatever% of anything is just (whatever/100) * anything.
800+1250+120+625+65 gives us 2860.
now, she doesn't get any commission from the 2000, just the surplus, the 860.
how much is 15% of 860? well is just (15/100) * 860.
The answer is either to change the - 1 to 0, or to add + 1 to it next to the - 1.
