单选题

ADVANCED PURCHASE DISCOUNTS FOR AIRLINE TRAVEL
Days Prior to Departure	Percentage Discount
0～6 days	0%
7～13 days	10%
14～29 days	25%
30 days or more	40%

The table above shows the discount structure for advanced purchase of tickets at a particular airline. A passenger bought a ticket at this airline for$1,050. The ticket agent informed her that, had she purchased the ticket one day later, she would have paid $210 more. How many days before her departure did she purchase her ticket?
(A) 6 days
(B) 7days
(C) 13 days
(D) 14 days
(E) 29days