The manager of a campus bookstore finds that in the last hour before closing, 41 students bought two or more textbooks. Of these 4 used cash only, 5 used a financial aid voucher only, and 5 used a debit card only. Seven used a debit card and financial aid voucher and no cash; three used cash and debit card with no financial aid assistance. Sixteen students total used a debit card for a least part of their purchase, while 9 used none of those forms of payment. (a) How many students used all of cash, debit card, and financial aid voucher?
(b) Did more students use cash or financial aid vouchers?
(c) What percentage of students did not use a financial aid voucher?