To answer this question, we must assume that she will be overpaying the amount if it passes any multiple of 50$ ie. Can't pay 60$ with a 50$ bill.
So we add all the costs:
$95 + $225 + $275 + $155 + $60 + $75 = $885
We divide out 885 by 50, to see how many 50$ bills we need.
885 / 50 = 17 bills with Remainder of 35.
Since we still need to pay for the 35, we need an additional $50 bill.
Thus: 17 + 1 = 18 bills.