A travel agency gives following discounts to their customers as follows:-

0-6 days in advance - 0%

7-13 days in advance- 10%

14-25 days in advance- 25%

A persons pays $ 1050 for his ticket.Had he purchased the ticket 1 day later, he would have paid $210 more.How many days before did he purchase the ticket?

Can someone help me solve this problem?