How would you best describe the phrase 2/10 n/30?

Select one:

a. 2 customers have 10 invoices; any number of customers have 30 invoice

b. 2 days to pay 10% of the invoice, 30 days to pay the rest

c. For two days, the company offers a 10% discount, a negotiated amount of discount can be obtained if paid within 30 days

d. 2 percent discount if customer pays within 10 days; if not paid within 10 days, payment is due within 30 days